(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Problems in biology"

,.)[■• Il."f ' I 



V 1 

\ 



; . : ; 



m 

■ 

m 

lip 

1 1 



Rgra/Tf ; 



I 



1 
I 



570 



BOOK 570.H917 c. 1 

HUNTER # PROBLEMS IN BIOLOGY 



3 T153 001373b5 S 



i t may 




Frontispiece 



Photo by H. Armstrong Roberts 



Biology is the study of plants, animals, and human beings. The out-of-doors is the best 
classroom and, although the school laboratory has to be used for class work, one can go to 
nature to confirm the truths that are learned from books and experiments. 



PROBLEMS IN BIOLOGY 



BY 
GEORGE W. HUNTER, PH.D. 

Lecturer in Methods of Education in Science 

ont Colleges and University of Southern California 

Los Angeles, California 

Formerly Head of the Department of Biology 

Dewitt Clinton High School, New York 




AMERICAN BOOK COMPANY 

NEW YORK CINCINNATI CHICAGO 

BOSTON ATLANTA 



5T 



COPYEIGHT, 1931, BY 

AMERICAN BOOK COMPANY 

All rights reserved 



H. BIO. 
W. P. 10 



MADE IN U.S.A. 



PREFACE 

The modern textbook in elementary science must do several 
things. First of all, it must contain enough subject matter to 
permit a rather wide choice of material ; this because of differences 
in the environment in which the book is used. Obviously every 
teacher of biology would like a text that interprets the particular 
environment in which the teaching is done, but since this is an 
impossibility the solution of the problem is a wide choice of topics. 
This text gives a large selection of informational material. 

Second, the modern text must give to the teacher a variety of 
problems, demonstrations, projects, and exercises for the workbook 
in order that the need of the individual student may be adequately 
met. Nothing is more difficult for the overloaded teacher than to 
attempt to adjust the work to the individual needs of a large num- 
ber of pupils. This book, with its many exercises and questions, 
graded to the needs of a heterogeneous group, squarely meets the 
problem of individual variation. Projects, demonstrations, and 
reports are suggested also in sufficient numbers to fill the time of a 
widely diverging group. 

Another thing the modern text should do is to give the student 
adequate help in testing his own factual knowledge and his own 
organizing ability. Self-testing devices are useful toward this 
end. All of the units included in the text have such devices. 
Formal summaries are purposely omitted. Instead, outline sum- 
maries, to be completed by the pupil, are used. 

This book follows the approved unit structure, and each unit is 
built on a general plan which has been tested and found to give 
satisfactory results. The unit is introduced by a number of survey 
questions intended to interest the group in the work which follows 
and to give the teacher an opportunity to find out what " apper- 
ceptive mass " exists in the minds of the pupils. This device may 



VI PREFACE 

be used to organize the work of superior students who have a basic 
knowledge of the material of the unit and who may therefore be 
allowed to organize some project as their share of the class work. 
The preview follows, giving a brief introduction to the problems of 
the unit, and is both an organizing and a motivating device. Next 
come the problems, many of which are introduced by laboratory 
exercises or demonstrations, with opportunity for individual work 
where it is practical. Numerous exercises and problem questions 
give opportunity for individual pupil assignments and reports. 
The organization of the unit by the pupil is provided for in the 
outline summaries, in the attainment tests, in individual check-up 
on the answers to the survey questions, and in the self-testing 
exercises. In these ways the teacher has an opportunity for 
individual work with students. The recitation period may consist 
of individual reports on rather large blocks of the unit, interspersed 
with rapid-fire questions where it is obvious that the student 
organization of the topic has left unexplained some vital point. 
The author wishes to thank the following for their critical 
reading of the manuscript in its entirety or in part or who have 
made valuable suggestions: Charles W. Finley, State Teachers 
College, Upper Montclair, New Jersey; Frank M. Wheat, Head 
of Department of Biology, George Washington High School, New 
York; Paul B. Mann, Evander Childs High School, New York; 
Ada L. Weckel, Head of Department of Science, High School, 
Oak Park, Illinois; Annah P. Hazen, Head of Department of 
Biology, Eastern District High School, Brooklyn, New York; 
and George W. Hunter III. Thanks are also due Loran W. Kitch, 
Herbert Hoover High School, Glendale, California ; Roy Knapp, 
Burbank Junior High School, Miss Beatrice Cayo, Elsinore High 
School, Elsinore, California; Mrs. Karyn B. Sanders, Downey 
Union High School, Downey, California; and Wright Pierce, 
Claremont, California, who have read the proof and given sugges- 
tions on teaching devices. 



TABLE OF CONTENTS 

PAGE 

WHY AND HOW WE STUDY BIOLOGY . . . . . 1 

PART I 

LIVING THINGS IN RELATION TO EACH OTHER 
AND THEIR SURROUNDINGS 

UNIT I. THE WORLD WE LIVE IN AND WHAT WE 
TAKE FROM IT 

PROBLEM 

I. What Does a Tree Take from Its Surroundings? . . 21 
II. What Are the Building Materials of the World and 

How Are They Used? 23 

III. What Are Foods and How Are They Used? ... 30 

IV. How Does Man Control His Environment? ... 32 

UNIT II. WHAT IS BEING ALIVE? THE FUNCTIONS 
OF LIVING THINGS 

I. What Do We Mean by Reactions to Stimuli? ... 39 

II. How Are Living Things Alike and How Do They Differ? 43 

III. What Are Cells and How Do They Produce Others? . 46 

IV. What Do We Mean by Adaptation? 49 

UNIT III. HOW ARE PLANTS AND ANIMALS 
MUTUALLY DEPENDENT? 

I. What Are the Inter-relationships of Plants and Animals? 57 
II. To Know Something of the Structure and Life History 

of the Grasshopper 62 

III. To Know Something about the Structure and Life 

History of the Butterfly 65 

IV. What Do We Mean by Communal Life and Division 

of Labor? 69 

V. What Are the Characteristics of Other Groups of Insects ? 75 
VI. Why Are Insects So Numerous? . . . . . .80 

VII. Of What Use Are Flowers to Plants? .... 83 

VIII. How Are Fruits Formed? .86 

IX. What Are Some Adaptations in Insects for Carrying 

Pollen? 88 

X. What Are Some Specific Examples of Cross Pollination? 91 

vii 



V1U TABLE OF CONTENTS 

UNIT IV. HOW AND WHY DO SEED PLANTS 
SUCCEED IN LIFE? 

PKOBLEM PAGE 

I. What Are Weeds and What Do They Do? . . . 101 

II. Why and How Should Weeds Be Eradicated? . . . 105 

III. How Are Fruits and Seeds Scattered? .... 108 

PART II 

GREEN PLANTS MAKE THE FOOD OF THE WORLD 

UNIT V. WHY DO SEEDS GERMINATE? 

I. Where Are Baby Plants Found? 116 

II. What Are the Tests for the Organic Nutrients? . . 118 

III. What Factors Are Necessary to Awaken the Embryo 

within the Seed? 120 

IV. What Becomes of the Parts of the Embryo during Its 

Growth into a Young Plant? 122 

V. What Makes a Young Plant Grow? 123 

VI. Where Is the Food Supply of Different Seeds? . .125 
VII. How Does the Corn Grain Make Use of Stored Food? . 128 

UNIT VI. GREEN PLANTS AS FOOD MAKERS AND 
FOOD USERS 

I. What Do Plants Take from the Soil? . . . .137 

II. What Factors Influence the Growth of Roots? . . 140 

III. How Does the Structure of a Root Fit It for Its Work? 143 

IV. How Do Root Hairs Take in Water and Soil Salts? . 147 
V. What Purposes Do Roots Serve? . . . . . 150 

VI. Where Does the Green Plant Manufacture Food? . 151 

VII. What Raw Materials and Conditions Are Needed to 

Make Food? 154 

VIII. What Are the Products and Results in Food Manu- 
facture? 160 

IX. How Is Food Circulated in the Plant? .... 166 

X. Why Are Plants Modified? 172 

part in 

RELATIONSHIPS AND INTER-RELATIONSHIPS 
OF LIVING THINGS 

UNIT VII. THE PLANT WORLD AND HOW IT 
AFFECTS MANKIND 

I. How Do We Classify Plants? 179 

II. What Are Bacteria and Where Are They Found? . .181 



TABLE OF CONTENTS 



IX 



PROBLEM 

III. What Are Some Useful Things That Bacteria Do? 

IV. What Are Yeasts and What Do They Do? 
V. To Learn about Some Destructive Fungi . 

VI. What Are Molds? What Do They Do? . 

VII. What Are Some Examples op Common Algae? 

VIII. What Is the Life History of a Moss Plant? 

IX. What Is the Life History of a Fern Plant? 

X. What Are Some Examples of Spermatophytes? 



PAGE 

186 
190 
193 
198 
200 
202 
204 
205 



I. 
II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI. 



UNIT VIII. HOW DO WE CLASSIFY THE ANIMALS? 

What Are the Characteristics of One-celled Animals? 
What Are the Characteristics of Some Simpler Inverte- 



brates 



What Are the Characteristics of the Arthropods? 
What Are the Characteristics of the Mollusks? 
What Are the Characteristics of the Fishes? . 
What Are the Characteristics of Amphibians? 
What Are Characteristics of the Reptiles? 
What Are the Characteristics of Birds? . 
What Are the Characteristics of Mammals? 
What Story Is Told by the Fossils? . 
What Is Man's Place in Nature? 



217 

223 
232 
240 
242 
250 
256 
260 
268 
271 
274 



UNIT IX. WHAT EFFECTS HAVE THE SURROUND- 
INGS ON THE LIVES OF PLANTS AND ANIMALS? 

I. What General Biological Relations Exist between 

Plants and Animals? 282 

II. What Do We Mean by the Nitrogen, Oxygen, and 

Carbon Cycles in Nature? 285 

III. What Is Symbiosis and How Does It Differ from 

Parasitism? 287 

IV. How Does Man Disturb the Balance of Nature? . . 289 

V. How Do the Factors of the Environment Affect 

Ecological Relationships? 290 

VI. Why Do Plants and Animals Form Communities? . . 298 

VII. What Is an Ecological Succession? 300 

VIII. What Do We Mean by Geographic Distribution of 

Living Things? 305 



X TABLE OF CONTENTS 

PART IV 
THE BIOLOGY OF MAN 

UNIT X. HOW DOES THE HUMAN MACHINE DO ITS 

WORK? 

Problem page 

I. What Is the General Structure of the Human Body? 314 

II. What Is the Structure of the Skin? 316 

III. What Is the Relation of Muscles to Bones? . . . 318 

UNIT XL HOW DOES MAN DETERMINE THE 
VALUES OF FOODS? 

I. What Do Foods Do for Us? 327 

II. What Do Vitamins Do for Us? 333 

III. What Is the Relation of Work, Environment, Age, 

Sex, and Digestibility of Foods to Diet? . . . 335 

IV. What Is the Best Proportion of Nutrients for Our 

Daily Diet? 340 

V. What Is the Daily Calorie Requirement? . . . 343 
VI. How Can the Relative Cheapness of Foods Be Deter- 
mined? 345 

VII. What Is Adulteration? 348 

VIII. What Is the Truth about Stimulants and Narcotics? . 350 

IX. How Does the Pure Food and Drugs Act Work? . . 355 

UNIT XII. HOW IS FOOD PREPARED FOR BODY USES? 

I. What Is a Gland and How Does It Do Its Work? . . 361 

II. What Is the Structure and Work of the Mouth Cavity? 363 

III. What Are the Parts of the Digestive Tract? . . . 367 

IV. What Digestive Changes Take Place in the Stomach? . 369 
V. What Work Is Done by the Pancreas? .... 373 

VI. What Are the Functions of the Liver? .... 375 
VII. How Are Foods Absorbed and How Do They Get into 

the Blood? 376 

UNIT XIII. HOW ARE FOODS CIRCULATED AND 
USED IN THE BODY? 

I. What Is the Composition and What Are the Uses of 

Different Parts of the Blood? 386 

II. What Are the Functions of Some of the Endocrine 

Glands? . . . .392 

III. How Does the Blood Circulate through the Body? . 395 

IV. What Is Respiration? 403 

V. What Are the Mechanics of Breathing? .... 406 



TABLE OF CONTENTS XI 

PROBLEM PAGE 

VI. What Are the Reasons for, and the Best Methods op 

Ventilation? 409 

VII. What Are the Organs of Excretion and How Do They 

Function? 411 

UNIT XIV. HOW HAS MAN BECOME THE CON- 
QUEROR OF THE WORLD? 
I. What Are the Chief Responses of Plants and Animals? 422 
II. How Do Simple Plants and Animals Respond to Stimuli? 424 

III. What Are Sense Organs and What Do They Do? . . 427 

IV. How Is Man's Body Controlled? 429 

V. What Part Do the Sense Organs Play in the Control 

of the Body? . 435 

VI. What Behaviors Are Instinctive? 441 

VII. How Are Habits Formed? 443 

VIII. What Are Some Good Health Habits? .... 447 

IX. What Are Some Effects of the Drink Habit? . . . 449 

PART V 

MAN'S INTER-RELATIONSHIP WITH OTHER 
LIVING THINGS 

UNIT XV. HOW DOES MAN CONTROL HIS ENVIRON- 
MENT FOR HEALTH? 

I. How May We Control the Growth of Bacteria? . . 457 

II. How Do Bacteria Cause Disease? 461 

III. How Do We Get Bacterial Diseases? .... 463 

IV. Why Is Quarantine Necessary? . . . . . . 471 

V. What Is Immunity? 474 

VI. What Are the Differences between Active and Passive 

Immunity? 476 

VII. How Is Malaria Caused and Transmitted? . . . 482 
VIII. How Was the Cause and Control of Yellow Fever 

Discovered? 487 

IX. What Are Other Disease Carriers and What Diseases 

Do They Carry? 489 

X. What Diseases Are Caused by Worms and How May 

We Fight Them? . . . 492 

XL How May We Improve Conditions at Home? . . . 497 
XII. How May We Improve Conditions at School? . . .501 

XIII. How May We Help Improve Conditions in Our Com- 

munity? 503 

XIV. What Protective Health Agencies Should Exist in a 

Community? 507 



Xll TABLE OF CONTENTS 

UNIT XVI. HOW DOES MAN CONTROL HIS EN- 
VIRONMENT FOR WEALTH? 



I. How Are Plants Used as Food? 520 

II. What Are Other Economic Values of Plants? . . . 528 

III. What Is the Value of Animals as Food for Man? . . 530 

IV. What Are Other Economic Values of Animals? . . 537 
V. What Harm Is Done by Animals? 544 

VI. What Is the Economic Importance of Birds? . . . 547 

VII. How Can We Recognize Some Common Birds? . . . 551 

VIII. What Is the Economic Importance of Insects? . . 560 

UNIT XVII. HOW DOES MAN CONSERVE HIS 
NATURAL RESOURCES? 

I. What Are the Values of Trees? . . . . 574 

II. Why Is the Conservation of Forests Necessary? . . 579 

III. What Is Being Done for the Conservation of Fish and 

Other Aquatic Animals? . . . . . . . 587 

IV. What Is Being Done for the Conservation of Birds? . 594 
V. What Is Being Done for the Conservation of Mammals? 598 

VI. How Is Conservation Applied to Man? .... 599 

UNIT XVIII. HOW DOES MAN CONTROL THE IM- 
PROVEMENT OF LIVING THINGS? 

I. How May Environment Affect Plants and Animals? . 608 
II. How Do Living Things Reproduce and Develop? . .611 

III. What Are the Laws of Heredity? ..... 620 

IV. What Determines Heredity? 626 

V. How Are New Varieties of Plants and Animals Pro- 
duced? 631 

VI. How Do the Laws of Heredity Apply to Man? . . 636 

UNIT XIX. HOW MAY BIOLOGY AID IN MY OWN 
IMPROVEMENT? 

I. How Can I Choose a Vocation? 646 

II. For What Vocations May Biology Help Prepare Me? 649 

UNIT XX. WHO ARE SOME OF THE MAKERS OF BIOLOGY? 

I. Who Were Some Early Workers in Biology? . . . 657 

II. Who Were Some of the Conquerors of Disease? . . 659 

III. What Are Some Great Names in the Study of Progres- 

sive Development? ........ 665 

IV. What Are Some Great Names in Natural History? . 668 
V. What Are Some Great Names Connected with Plant and 

Animal Breeding? 670 



WHY AND HOW WE STUDY BIOLOGY 

The study of biology. The word biology comes from two Greek 
words, bios (life) and logos (word or study). Biology, then, is the 
study of things that are alive, both plants and animals. Man lives 
in a world filled with living things. Some are his friends and some 
are his enemies. It is essential, if he is to be master of this world, 
that he should understand the living things that are around him. 
His mastery is due to his understanding of the processes of life in 
nature. There are many ways in which this conquest is achieved. 

Biology in relation to health. It is most important that we 
control the living things that harm our health. We live in a 
world that is filled with tiny enemies — some in the water, some 
in the ground, some enricH. 

living on plants, some soil 

living on animals. We r ~, r<M , >•.,»,..**» 

o cause "RAf v 'TFDtA cctixse, 

call them parasites cfec^xy - * -dm.w.ckia — *- c ci 5 - ease 

because they take * \ 

nourishment from a cSSe 

living Organism and Some of the work done by bacteria. Can you add any 
■ I. • i others not given in the diagram ? 

give nothing m return. 

The smallest and yet most widespread of these parasites are the 
tiny bacteria or germs existing almost everywhere about us, in 
water, soil, food, and air. They play a tremendous part in shaping 
the destiny of man. They help him in that they act as scavengers, 
causing things to decay; they give flavor to cheese and butter; 
they assist the tanner ; and they are invaluable aids to the farmer. 
But, on the other hand, they cause the decay of meat, fish, vege- 
tables, and fruits; they sour milk and sometimes spoil canned 
goods; more than this, they cause diseases such as diphtheria, 
tuberculosis, and typhoid fever. 

Hundreds of scientists are devoting their lives to the study of 
germs and their control, which makes up that subdivision of biol- 
ogy known as bacteriology. A great bacteriologist, Louis Pasteur, 

1 



2 WHY AND HOW WE STUDY BIOLOGY 

once said, "It is within the power of man to cause all parasitic 
diseases to disappear from the world." This prophecy is gradually 
being fulfilled. It is estimated that from 75 to 90 per cent of all 
sickness is preventable and that the economic loss in the United 
States each year from disease and death is about $3,000,000,000. 
This loss could be largely prevented if we were willing to use the 
knowledge we now have in the methods of controlling and ex- 
terminating disease. It may be the lot of some boys and girls 
who read this book to do their share to bring about this condition 
of affairs. 

The economic values of biology. There are other reasons why 
we should know something about biology. Plants and animals 
can live together on the earth only because food is supplied by 
green plants. Probably many of us do not realize that if all 
the green plants were gone from the earth there would be no 
animals. We shall see later why this is true. We all know that 
man's food supply is determined very largely by his ability to 
grow and develop plants that produce food for him and for the 
animals which he eats. 

Plants and animals are useful to man in other ways than for food. 
He uses, for clothing and ornaments, animal products such as wool, 
fur, leather, hides, ivory, coral, and mother-of-pearl. Plants also 
provide him with many kinds of building materials. Much of his 
clothing, and the thread with which he sews it, come from plant 
fibers. In hundreds of ways plants are made use of in the arts and 
trades. It is the duty of every boy and girl to know something of 
these uses. 

The conservation of our natural resources. Still another reason 
why we should study biology is that we may work intelligently for 
the conservation of our natural resources, especially our forests. 
The forest, aside from its beauty and its health-giving properties, 
holds water in the earth. It keeps the water from evaporating 
from the soil on hot days and from running off the surface on rainy 
days. Regions that have been deforested, such as parts of China, 
Italy, and France, are now subject to floods, and are in many 
places barren. Our supply of timber and to a large extent our 
future water power depend on the forests. 



VALUE OF BIOLOGY 3 

Vocational knowledge. Sooner or later the boys and girls who 
read this book must think of the kind of work they are going to do. 
Selecting a vocation is one of the most important decisions that 
one will ever have to make. Through a study of biology you will 
learn something about such professions as medicine, nursing, 
forestry, agriculture, or the teaching of science which might 
appeal to you as worth-while vocations. Your teacher may give 
you the inspiration which will determine your future career. 
Many years ago, a professor in college inspired me to become a 
teacher of biology and I have never regretted my choice. Perhaps 
you will be as fortunate. 

Use of leisure time. It is a wonderful world we live in, but not 
many of us know how to enjoy it fully. Many boys and girls of 
today think that they are getting all there is out of life if they go 
regularly to the " movies " or meet with their crowd at games or 
parties. But no one has really got very much out of this world 
until he or she has learned, among the other things, the fun of 
hiking, of collecting, of observing nature, of taking trips to the 
shore, to the canyon, and up a mountain with an end in view. 
The interest that comes in observing and collecting insects or 
flowers makes life much more worth while. A study of biology 
will give one the information and incentive for such excursions. 

Reading values of biology. The papers and magazines of today 
contain many discussions and stories which deal with biological 
subject matter. The daily paper has its column of health hints, its 
stories of animal doings, and its statistics about animal and plant 
products. The average person with no biological training reads 
without being able to judge of the truth contained in these state- 
ments. The study of biology ought to give us some knowledge 
and should certainly show us where to go for accurate information 
so that we can tell whether our newspaper " science " is true or 
false. It will also open to us a wealth of books which are accurate 
and fascinating to read. The names of such books are given from 
time to time in the pages which follow. 

Open-mindedness a by-product. There is no doubt that in 
spite of living in an age which is noted for its products of scientific 
thinking, many people are satisfied to have others do their 



4 WHY AND HOW WE STUDY BIOLOGY 

thinking for them. They believe almost anything they are told 
without taking the trouble to investigate the truth of it. Politi- 
cians are able to lead the public around by the nose, because 
people are too indolent to find out the truth for themselves. The 
study of science ought to make young people disgusted with such 
lack of thinking. After one has experimented, observed, and read 
about scientific findings and facts he is not so easily fooled and 
he wants to be shown, not told. This open-mindedness should 
come through the study of science. A boy or girl who has learned 
to think straight will be more likely to five straight and be just 
that much more worthy a citizen of tomorrow. 

Biology in its relation to society. The study of biology should 
be part of the education of every boy and girl, because society itself 
is founded upon the principles which biology teaches. Plants and 
animals are living things, each taking what it can from its sur- 
roundings; they enter into competition with one another, and 
those which are the best fitted for fife outstrip the others. Health 
and strength of body and of mind are factors in man which tell in 
winning. The strong may hand down to their offspring the 
characteristics which make them the winners. An understanding 
of the laws of heredity ought to make each one of us better able to 
assume the duties of parenthood, duties which all too often are not 
understood by the boy and girl of today. 

Biology should develop character. Finally, if one studies 
biology with earnest purpose he cannot help but gain in moral and 
ethical character through the unfolding of truth and the knowledge 
gained of the working of the laws of nature in the everyday world 
around us. As Shakespeare once said, # a seeker in the great out-of- 
doors : 

" Finds tongues in trees, books in the running brooks, 
Sermons in stones, and good in everything." 

Where we should study biology. In a modern high school a 
good deal of time is spent by boys and girls in outside activities — 
athletics, dramatics, debating, and the like ; but too little emphasis 
has been placed on some outside interest that might come directly 
from the study of biology. Although we must be in the schoolroom 
much of the time, the ideal place to study biology is out-of-doors, 



WHERE WE SHOULD STUDY BIOLOGY 5 

for as one biologist once said, " The place where a plant or animal 
lives is just as important as the plant or the animal itself." One of 
the most interesting lessons I ever saw taught was given in a vacant 
lot near a high school in the city of Chicago — a place that seemed to 
have little in it except weeds and piles of refuse. But the teacher 
knew the possibilities of that lot, and the pupils were having a 
wonderful time studying the living things which they found there. 




Photo by Shipp — U. S. Forest Service 
These surroundings make an ideal outdoor laboratory. Why ? 

Some were watching the activities of an ant colony, while others 
were watching to see how a spider built a geometrical web. Every 
boy and girl in the group had a problem that was most interesting 
to him or her. But how much more interesting might be a trip 
to a canyon or a meadow brook or a sea beach ! For some of us 
this might be possible at almost any time. 

But if we cannot go to the field for study, then we can bring the 
field to the laboratory or schoolroom. If each member of the class 
would bring in some small living things and would arrange to care 

H. BIO — 2 



6 



WHY AND HOW WE STUDY BIOLOGY 



for them, the schoolroom would soon be a place much like the 
out of doors. A balanced aquarium may be started and observa- 
tions can be made on the life developing there. One can grow 
plants and learn how to take care of them. One might bring in all 
sorts of living things and keep them in a vivarium. The labora- 
tory becomes a place for studying nature at first hand, and that is 
what makes biology interesting. 




Students at work in an indoor laboratory. What are some of the good features in this 

laboratory ? 

In some communities it is possible to have a plot of ground near 
the school which can be kept as an experimental garden. Here 
much can be learned about plants, their care, and their insect 
friends and enemies. 

Some interesting activities. Another way to maintain interest 
in biology is to form a hiking and collecting club. There are so 
many interesting things to do in the field. One can make collec- 
tions of local plants, flowers, or insects. A school museum can 
be started, and one can always have a good deal of fun trying to 



INTERESTING ACTIVITIES 7 

identify new forms. Trips to various localities will help us under- 
stand why some animals and plants thrive there while others are 
found in different places, and to know what kinds of living things 
to expect in different places — under stones, under the barks of 
trees, in the water, and in galls on leaves. All these places and 
many more harbor animals, usually insects. 

Another interesting experience that some can have is that of 
collecting fossils, which are the evidence of life in times past. 
Many parts of the country have fossil remains, and it is very easy 
to get some local expert in geology to help you label your findings. 
Start a collecting club and exchange specimens with boys and girls 
in other localities. Thus you can do a good piece of constructive 
work for your school by adding to the school museum. You will 
be surprised to find many people who are willing to help you in this 
work. 

Have you a biology club in your school ? If not, then organize 
one at once, using 10 to 20 of the most interested members of your 
classes as a nucleus. This organization will help keep interest in 
the work and will later in the year be of much help in presenting 
demonstrations and projects, in planning exhibits and in helping 
in the care of the living things in the laboratory. Such a club can 
take charge of the school collections, help classify them, and add to 
them when possible. 

How to prepare for a field trip. The boy or girl who will go 
afield must do several things to prepare for the trip. Chief 
among these is to get or prepare collecting nets, insect killing 
bottles, collecting boxes, and spreading boards. Field trips will 
be of most value if materials are found and brought back for later 
study in the school laboratory. 

How to make an insect net. An insect net can easily be made 
in the following way: Cut a 36-inch piece of stout wire (#12 
spring brass wire is good), bend it into a loop nine to twelve inches 
in diameter, and then twist the ends and bend them so that they 
will lie in two shallow grooves which have been made in an old 
broom handle. Fasten the wire in place with fine wire twisted 
tightly around the end of the broom handle at the place where the 
two heavy wires He along the grooves. Make a net of cheesecloth 



8 



WHY AND HOW WE STUDY BIOLOGY 



or bobbinet, which should be 18 inches deep and large enough to go 
over the loop. Such a net can be used for catching flying insects, 
for dredging or scraping insects out of long grass, and for dipping 

insects or other small 
animals out of shallow 
ponds or brooks. 

The cyanide bottle. 
Cyanide of potassium 
fumes are best for kill- 
ing an insect quickly. 
Since, these fumes are 
deadly to man as well 
as other animals, such 
a bottle must be 
handled very carefully. 
To make a cyanide 
bottle, take a wide- 
mouthed bottle of 
about 6 to 8 ounces 
capacity, and place in 
it two or three pieces 
of cyanide of potas- 
sium the size of a chest- 
nut. Do not breathe 
the fumes ! Cover at 
once with sawdust and 
pour in liquid plaster 
of Paris to a depth of 
about one inch. The plaster will harden quickly. Cork the 
bottle tightly and keep it closed except when placing insects in- 
side. Label the bottle like that in the diagram so that you will 
know it contains a poison. 

Collecting water forms. Some of the members of the party should 
have quart jars so that living water animals may be captured and 
brought back alive. Be sure to collect with the fish, frogs, or water in- 
sects a small amount of some of the green plants growing under water 
so that you may have living plants to start a balanced aquarium. 



#12 
"brass 




clo-Ux. 



Read your text and then explain the figure. Can you sug 
gest any other ways to make an insect net? 



HOW TO PREPARE FOR A FIELD TRIP 



9 




t>o not ■r™ 5 

5 »NHAL6 Z: 




-plaster 

of Pans 

-sccwcftcst 

-lixmps of 
cycrnxdus. 



Why do we cover the cyanide with 
plaster of Paris? 



Collecting boxes. After killing in the cyanide bottle, the 
insects, if butterflies or moths, may be wrapped in little pieces of 
stiff paper which are folded in triangu- 
lar form so as to fit the shape of the 
wings. But a collecting box should be 
made to hold some of the specimens. 
A cigar box, with a sheet of quarter- 
inch cork glued in the bottom, and a 
supply of insect pins are all that is 
necessary. 

Spreading insects . To prepare winged 
insects for mounting it is necessary to 
spread their wings out. While the 
specimen is still flexible, pin it down on 
a thin board of soft pine or cigar box 
wood by placing insect pins close to the 
sides of the body, not through it, then 
pull the wings out flat and hold them 
down to the board with pieces of glass until they are dry. Place a 
small piece of pith between the legs so as to keep them in a natural 
position. When the insect is dry, you can mount it on a pin, and 
place it on cork in a case not over an inch or so in depth. Boxes 

having glass tops, in which certain 

_^ \ brands of chewing gum come, may 

be obtained for this purpose or boxes 
may be made in the manual train- 
ing department of the school. 

The art of preparing caterpillars 
by blowing is described in Hodge's 
Nature Study and Life or in any good 
book on entomology. Why not try 
this as a future project? 

Mounting your insects. After the 
trip is over, the insects may be dried 
carefully and then placed in Riker 
mounts if such are available, but 

A spreading board. Explain, after read- ' 

ing your text, the use of this board. homemade mounts are not difficult 




10 WHY AND HOW WE STUDY BIOLOGY 

to make. Get two plates of glass of the same size, 4X5 inch 
negatives will do. Cut thin strips of wood, not thicker than the 
largest specimen you wish to mount, glue to one piece of glass, then 
fasten your insect in place on the glass with a tiny drop of glue f 
using, if possible, a bit of the dried plant upon which it was 
feeding as a part of your mount. The other glass may then be 
placed on the wooden sides and the whole thing permanently 
sealed by binding around the edges with bicycle tape or passe 
partout paper. Life histories of insects can be worked out in such 
cases and can be handled readily, which makes them very useful in 
class work. 

An ants' nest. An ant colony makes a fascinating study for the 
schoolroom. To make a suitable nest take a piece of roofing slate 
or a flat tile, glue to it pieces of wood about a quarter inch high so 
as to make an oblong area six by eight inches or larger, with two 
little openings between the wood strips; get a piece of window 
glass to fit over it and then place the slate in a shallow tray which 
will hold water and will make a moat around your colony of ants, 
which may easily be found under flat stones. Take a small 
trowel and, when the colony is found, scrape up as many of the 
eggs, larvae, and ants as possible. Be sure to get one or more of 
the winged queens by digging down into the nest. Take your 
colony home in a well-corked bottle, dump the contents into your 
prepared nest, smooth down the earth, and place the glass over the 
top. Cover it with a black cloth or some opaque object so as to 
exclude the light. Within a day or two the life of the colony will 
be quite normal and you can study the ants at leisure. Feed them 
from time to time by placing sugar or crumbs of bread just outside 
the wood strips. 

An insect cage. Frequently we wish to bring living insects into 
the laboratory in order to study their feeding or other habits. For 
this purpose an insect cage may be made by taking a shallow flower 
pot in which earth and some green plant has been placed. Cover 
this with a lamp chimney having a bit of cheesecloth placed over 
the top. If the plant within the pot is a food plant and is kept 
watered, it will be possible to keep the captured insects alive for 
a considerable period of time. 



A BALANCED AQUARIUM 



11 



Practical Exercise. What insects found in your locality might be kept in 
the lamp chimney cage? 




^ 



m 



wg 



moke cc "box 
-v/ith strips 
for* sic(es,ct 
Hngect coyer 
anct cc ^olicC 
teocse 



ft~t r 



i 





cover open, 

sides -N^th— 

wire screen. 



A homemade insect cage. Make 
the uprights about 24 inches and the 
sides of the cage 18 inches wide. 
Place a shallow pan in the bottom, fill 
it with earth, and put in plants on 
which the insects may feed. 



A balanced aquarium. Frequently, trips may be made to a 
stream or pond. In such an event, collect snails and other small 
mollusks by scraping the muddy bottom of the stream with your 
dip net. Catch any fish that you can with insect larvae, small 
water beetles, water striders, or other forms of insect life. Be sure 
to collect several kinds of water plants, especially those with green 
leaves under water. 

Use as your aquarium a large clear glass jar of any shape, and 
cover the bottom with smooth pebbles. Fasten the water plants 
down by tying small weights to the base of their stems. Use pond 
water for the aquarium, transferring the fish and other living 
things directly into it from the jars you brought them home in. 
Place the aquarium in a well-lighted part of the room, moving it 
away from the direct sunlight if the growth of the green plants 



12 WHY AND HOW WE STUDY BIOLOGY 

becomes too rapid. Add more snails if the sides of the aquarium 
become covered with a green growth. In this way, your aquarium 
will be kept in balance, which means that the plant life supplies the 
animals with food in sufficient quantity while the animals give the 
plants enough wastes to allow them to make food in the sun- 
light. The interesting story of how plants do this will be told 
later. 

Other interesting problems. Out of the field trips and the 
collecting of insects and other animals will come many other 
instructive problems. Some pupils may become interested in the 
classification of animals, others in making a survey of the locality 
to see where different animals are most plentiful, and others in the 
various ways in which animals protect themselves or are protected 
by their surroundings. In fact, there are so many problems that 
it will be almost impossible for us to note them all here. Let us 
now turn to some plant problems or projects that will come out of 
a fall field trip. 

Plant studies in the field. The fall of the year usually finds a 
good many plants in blossom, although most of these have com- 
posite blossoms. But flowers are not the only things to collect. 
A leaf collection can easily be made in the fall and mounted in the 
way suggested for insects, except that no wood need be used be- 
tween the plates of glass. Interesting mounts of skeleton leaves 
may be prepared by placing collected leaves in trays of water until 
the leaf tissue has rotted away, leaving the skeleton of veins and 
ribs as a delicate tracing. These make valuable aids in the 
laboratory study of leaves. Another interesting and easy method 
of obtaining good leaf illustrations for your notebook is to make 
blue prints of them. Weed and flower collections may be mounted 
in a similar manner. 

Some members of the class may become interested in making 
a collection of weeds, and some may wish to make a survey of 
weeds found in their locality. Weed eradication may be studied 
as well, thanks to the various government pamphlets which are 
easily obtainable. Many of us do not even know the trees com- 
mon to our neighborhood. A survey of trees might be conducted 
to determine where different types may be found and then sug- 



OTHER OUTDOOR ACTIVITIES 



13 



gestions might be made as to where trees could advantageously be 
planted in a town. Such a survey might result in real civic better- 




\0 



A collection of fern leaves made by high school pupils. 

ment. A survey of forest trees would be another interesting 
project. Planting and raising seedling trees is certainly another 
worth-while activity. 

Other outdoor activities. Birds are most plentiful in the spring 
and should then be studied out of doors. But birds can always be 
attracted to your own home by means of nesting boxes, drinking 
fountains, and by feeding stations. Photographing wild birds is a 
pleasure worth working for. A census of the number and kinds of 
birds that frequent your neighborhood and the kind of nests they 
build are interesting projects. Through bird trapping and band- 
ing much can be learned about the migrating and nesting of birds. 

Gardening. Gardening and the study of the life of some com- 
mon garden plants will interest some of us. Others may want to 
make a study of certain garden or other plant pests and how to 
eradicate them. Still another study might be that of the plants 
which do damage to crops or trees of our neighborhood. In short, 



14 WHY AND HOW WE STUDY BIOLOGY 

these pages have only begun to suggest some of the activities that 
will grow out of our study of biology. Most of these are things we 
can do out of school hours and they certainly are worth while from 
every viewpoint. 

The value of city surveys. Not all of the outdoor work is 
collecting, nor is the country the only place to make a field trip. 
We have spoken of studies in vacant lots and tree surveys in a city. 
Of still more practical importance are sanitary surveys which tell 
us of the sanitary conditions of our neighborhood. What are the 
conditions in the meat stores ? Are the goods there kept under 
sanitary conditions? Are the streets of your city well watered 
and cleaned? Are the garbage and ash collections regular and 
sufficient? Are the schools well lighted, properly heated, and 
effectively swept ? Are there efficient and well-kept playgrounds, 
baths, and parks? All these and more can be worked out in the 
field by a group of pupils of biology, thus proving that biology has 
a part in citizenship. A group of young people have more than 
once rid a town of mosquitoes or flies, just by makiDg a survey, 
discovering the sources of these pests, and then proceeding to 
eradicate them by the methods which they learned in biology class. 

Practical Exercise. How many of the above-mentioned things can be done 
by the members of your biology class ? Give reasons why they can or cannot 
be done. 

The use of the laboratory. It is said that on one occasion, John 
Hunter, a well-known Scottish physician, who was a teacher of 
Jenner, and lived from 1728 to 1793, was present at a discussion 
concerning the digestive system of birds. The meeting broke up 
without any decision and at the next meeting several persons 
brought quotations from the works of such old philosophers as 
Aristotle, Hippocrates, and Galen to prove their previous state- 
ments. But John Hunter brought in a dissected bird and showed 
the organs in their natural position. This naturally settled all 
arguments. 

Unfortunately we cannot do all of our work out of doors. We 
must use the laboratory, and of course we must take the authority 
of books. It goes without saying that if we were to spend our 



THE USE OF THE LABORATORY 



15 




time in rediscovering the hundreds of thousands of facts already 

known about plants and animals, we would not get very far with 

any new discoveries. So we 

rely on texts and reference 

books because they have been 

written by specialists, and in 

this way we may make an 

earlier start toward discoveries 

of our own. 

Biology, more than any sub- 
ject you are now studying, 
ought to prepare you to think 
logically. The method of the 
experiment is much like the 
steps of an act of real thinking. 
In our attempt to solve a prob- 
lem through an experiment we 
use four steps : first, we state 
our problem ; second, we do 
certain things to try to find out 
something about it ; third, we observe and analyze what we have 
done ; and fourth, we draw a conclusion as the result of what we 
have seen. These are the steps taken by any one who really 
accomplishes anything in the way of constructive work. But in 
an experiment, if we really want to prove our point, it is necessary 
to establish a control. For example, suppose we want to know 
what effect exercise has on the rate of our heart beat. We can 
first take the pulse rate when quietly sitting at our desk or when 
lying down, and then we can take a definite amount of exercise 
and again take the pulse rate. In this way we establish a contrast 
between the heart beat when we are at rest and when we have had 
exercise. The rate of the pulse when we are at rest is known as 
the control. Which of the two rates of the pulse just obtained 
would be of real value in giving us correct information about our 
normal heart beat? Experiments and projects with the proper 
controls will give us the techniques we need to be thinkers and 
doers in this world. 



John Hunter, a physiologist and surgeon, car- 
ried on much biological research. He always 
sought the truth through observations and ex- 
periments on lower animals. 



16 WHY AND HOW WE STUDY BIOLOGY 

Clear thinking should come from science study. Psychologists, 
the people who study the science of the mind, tell us that those of 
us who like and understand our work and make its ideals our own 
ideals get much more general value from its study than those who 
do not. If, for example, in science we consciously try to see why 
each step of an experiment is performed and actually practice the 
method of the experiment in other similar cases, we may carry over 
this method of thought to other subjects and even apply it in our 
daily life. The scientific method of thinking has resulted in new 
inventions, in discoveries, and in straight thinking the world over. 
Why not try consciously to apply our method of doing and think- 
ing in science to other kinds of doing and thinking in daily life? 
This would give us the greatest values from biology that we could 
hope to get. 

Method of use of this book. In the pages that follow, a regular 
procedure will be used which has been shown by actual experiment 
in schools to be one of the best ways to study introductory science. 
In the first place, our work is divided into units, each of which has 
some practical or definite relation to our own lives. Nothing has 
been included in the text that does not directly or indirectly in- 
fluence the lives of each one of us. 

Each unit is introduced by a series of survey questions which are 
intended to find out what you already know about the subject 
matter of the unit. This is followed by a brief preview, or intro- 
duction to the work of the unit, which will give you a bird's-eye 
view of the subject matter of the unit. It might be said to be a 
" selling " device by which each of you may become interested io 
the work of the particular section or unit. The preview is followed 
by a series of problems which explain the unit. Each problem 
usually includes demonstration or laboratory work, and enough 
text is given so that this laboratory work is explained. The 
references given at the ends of the units should be used when 
available. The problems will be largely your work, and your 
understanding of biology will depend largely upon your thorough- 
ness in the laboratory or field or library. At the end of each 
problem and at the end of the unit are certain self-testing devices 
which will help you to know whether you have mastered the 



METHOD OF USE OF THIS BOOK 17 

contents of the unit. When you have tested yourself, check back 
on the survey questions to see if you have any corrections to 
make there. After this is done you are ready to make your report 
to the class on the unit or such part of it as your teacher may 
assign to you. To prepare for this recitation make an outline 
summary for your workbook. This will help you to organize 
the material in the unit in the best possible way, and thus come 
to a complete understanding of the material contained therein. 
If you understand this plan of the book, you will be able to get 
better results in its use. 

The last unit in the book gives short and interesting stories about 
a few scientists who, by much work and perseverance, made 
remarkable discoveries that have so largely contributed to our 
knowledge of biology. The lives of these men may be studied in 
relation to the unit in which their work is discussed or they may be 
studied at the completion of the other units. 

Useful References 

Apgar, E. A., Trees of the Northern United States. (American Book 

Company, New York) 
Bailey, F. A., Handbook of Birds of the Western United States. (Houghton, 

Mifflin Co., Boston. 1921) 
Boulenger, E. G., Aquarium Book. (D. Appleton & Co., New York. 1926) 
Clements, E. G., Flowers of Mountain and Plain. (H. W. Wilson Co., 

New York. 1920) 
Comstock, J. H., and Comstock, A., How to Know the Butterflies. (Corn- 
stock Publishing Co., Ithaca, N. Y. 1920) 
Downing, E. R., Our Living World. (Longmans, Green & Co., New York. 

1924) 
Georgia, A. E., Manual of Weeds. (The Macmillan Co., New York. 

1914) 
Hodge, C. F., Nature Study and Life. (Ginn & Co., Boston) 
Hornaday, W. T., American Natural History. (Charles Scribner's Sons, 

New York) 
Lutz, F. E., Field Book of Insects. (G. P. Putnam's Sons, New York. 

1921) 
Needham, J. G., and Lloyd, J. T., Life of Inland Waters. (Comstock 

Publishing Co. 1923) 
Palmer, E. L., Field Book of Nature Study. (Comstock Publishing Co. 

1927) 
Thomson, J. A., Outline of Science. (G. P. Putnam's Sons. 1922) 
Waters, H. J,, Essentials of the New Agriculture. (Ginn & Co. 1924) 




Survey Questions 

Can you give the meaning of the term " environment " ? Is it correct 
for us to speak of our chemical environment ? Explain. What is the dif- 
ference between a chemical and a physical change? Do you know the 
chemical elements which are most common in your environment? What 
is a food? How would you define it scientifically? 



18 



PART I. LIVING THINGS IN RELATION TO 

THEIR ENVIRONMENT AND TO EACH 

OTHER 

UNIT I 

THE WORLD WE LIVE IN AND WHAT WE 
TAKE FROM IT 

Preview. In our previous experience with science in the 
elementary and junior high schools we have learned something 
about our environment and what we get out of it. We know a 
little about the air and how we use it, about water and how it 
serves us, of fire, of the weather, and many other useful facts that 
help us in our daily living. But now we are ready to learn some- 
thing more about this environment from a different angle. 

Biologists realize more than ever before that living things are 
dependent upon their environment and that they are composed 
of many of the chemical substances that are found in that environ- 
ment. Thus, our knowledge of biology depends upon an under- 
standing of the chemists' and physicists' conception of the world 
about us. This unit will help us to understand some of these 
important facts about our surroundings. The physicist calls 
anything that occupies space matter. The chemist in his turn 
reduces all matter into over ninety simple substances called 
chemical elements, substances that cannot be broken into more 
simple substances. These elements are given symbols by the 
chemist, such as O for oxygen, H for hydrogen, N for nitrogen, 
and C for carbon. The soil and other things in nature are com- 
posed largely of combinations of elements known as chemical 
compounds. A few of these compounds, such as water, iron rust, 

19 



20 



THE WORLD WE LIVE IN 



and table salt, are simple, inasmuch as they contain only two or 
three elements; but the greater number of compounds found in 
nature are very complex. The chemist uses several symbols to 
designate the binding together of elements into compounds. 
Several symbols together are known as a formula. For example, 
H 2 is the formula for water and indicates that two parts of hy- 
drogen combine with oxygen in a definite proportion by volume. 

. t1 , A chemical com- 

m blood Serum 



in sect v/fcxter* 



sodium. 



magnesium 
Calcium J? 
potassiunv 



chlorine 



SO* 

CO3 , 

bromine 3 



50.59 



3.73 



1.2, 



55.27 



7M 



r.2\ 
49 



39. 



45.- 



1<2. 



._ socCiu m 



magnesium 
—daidium 
•potassium 



.-Chlorine^ 



£o 3 

PzOs 

According to analysis, scientists have found that the per- 
centages of chemical substances in sea water are quite similar to 
those found in the blood serum (after Osborne). 



pound is a combina- 
tion of two or more 
elements in which 
each of the elements 
loses the character- 
istics which distin- 
guished it. For ex- 
ample, if fine iron 
filings and flowers 
of sulphur are 
mixed, each element 
will retain its own 
peculiar properties, 
can still be recog- 
nized, and can be 
easily separated by 
means of a magnet 
which will attract 
the iron. But, if the 



mixture is heated in a test tube, several important changes in the 
mixture will take place. A solid black substance is obtained 
which is not attracted by a magnet. The elements can no longer 
be separated by mechanical means. This black substance is a 
compound called iron sulphide. It has several properties quite 
different from those of either the iron or the sulphur. Rocks, 
humus, organic food substances, and the bodies of plants and 
animals are all composed of chemical compounds. 

Professor H. F. Osborne of Columbia University has pointed 
out that the chemical substances found in sea water correspond 



SURROUNDINGS OF A TREE 21 

very nearly with those in the human blood. There are other 
facts also which prove that some of the same chemical elements 
found in the environment somehow or other become organized 
into the tremendously complex material of which we find living 
plants and animals composed. 

PROBLEM I. HOW IS A TREE FITTED TO LIVE IN ITS 
NATURAL SURROUNDINGS? 

Field Exercise. Observe a tree in its natural environment. Bring in 
all the information you can to class concerning where a given tree grows, 
its form, size, characteristics, etc. The findings of the class can be 
tabulated on the board, and from this a general statement can be made 
concerning the characteristics of all trees. 

As Joyce Kilmer well said, there is no poem as lovely as a tree. 
Trees are so commonplace that we are not likely to consider what 
life would be without them. They grow straight and tall, even in 
cities where life for them must be very difficult. The problem 
before us is, " How do they do it ? " How can a tree (or any other 
green plant for that matter) develop into the great bulk that they 
have? They cannot make something out of nothing. It takes 
several acorns to weigh an ounce, but an oak tree weighs several 
tons. Where does this increase come from ? Evidently the young 
tree must take something from its surroundings in order to grow. 
What are the substances it uses? And how does it do this? 

The skeleton. Let us take a typical tree, such as the maple 
or elm. We notice in winter it is a skeleton, a straight trunk or 
main stem and many branching limbs which spread out into ever 
smaller and smaller branches. These are covered with buds which 
in spring will produce leaves or flowers or both. Under the 
ground we know there are roots, which, in the same manner as the 
branches, spread out widely and continually branch so that in 
many trees there is almost as much of the tree below ground as 
above it. Evidently the roots anchor the tree in the ground, 
while the branches place the buds and leaves in the most favorable 
position possible. 

Leaves. In the summer the tree is covered with green leaves. 
These, we notice, are set as far out as possible on the branches. 
Evidently sunlight influences them, for a bird's-eye view of the 
H. bio — 3 



22 



THE WORLD WE LIVE IX 




IT. BtowtuII 



An American elm in summer. 



tree shows that the leaves are placed so that they shade each other 
but little, and present their flat surfaces at right angles to the 
sun's rays. The leaves, as we shall later see, are food factories 

and do their work by 
energy received from 
the sun's rays. 

Roots. If we were 
to examine the roots, 
we would find here 
evidences that they 
take in water, besides 
anchoring the tree and 
giving it firm support. 
Trees growing near 
irrigating ditches or 
sewers often fill them 
with masses of fine 
roots which have 
sought out the water. 
The smaller rootlets 
are covered with tiny 
absorbing organs called 
root hairs. 

However, the tree 
must take other ma- 
terials than water from 
its surroundings in 
order to grow, for no 
thing can live and 
grow on water alone. 
Our problem now be- 
comes more difficult, and we cannot answer it completely. But 
we do know that the green plant, taking substances from the air 
and soil surrounding it, manufactures the material we call organic 
food, and uses this food to make its living material. 

To discover just what a tree takes from its surroundings involves 
the knowledge of some chemistry. Most of us have had some 




L. W. Brownell 
The same tree, as above, during the winter. 



BUILDING MATERIALS 23 

of this knowledge from a course in general science, but we must 
now review some of the elementary facts in order to answer the 
problems which follow. 

Self-Testing Exercise 

A tree has (1), (2), (3), and green 

(4). The (5) serve to anchor the tree in the ground 

and take in (6). The stem holds to the light the 

(7), which are the (8) (9). The tree 

takes (10) materials from its environment and makes them 

into (11) and (12) matter. 

PROBLEM H. WHAT ARE THE BUILDING MATERIALS OF 
THE WORLD AND HOW ARE THEY USED? 

Matter. Matter and energy are the fundamental things in the 
world. Matter is anything which has weight or occupies space. 
The tree is made of matter, as is the surrounding soil, the water, 
and even the air which it uses. Matter is usually present in one 
of three forms, a gas, a solid, or a liquid ; and, as we know, is capable 
of being changed from one form to another. For example, a 
liquid, water, may be changed into a vapor, steam, by heating, or 
into a solid, ice, by freezing. In biology, matter is usually thought 
of as being of two sorts, organic, or that which comes from living 
things, and inorganic, or the material that never has been alive. 

Energy. When a tree grows, or the roots push their way 
through the soil, or take in water, energy is being exerted. 
Energy means the power or ability to do work. There are five 
kinds of energy : mechanical, electrical, chemical, heat, and light 
energy. To perform its work the tree uses light energy, chemi- 
cal energy, and heat energy, which it may change into mechanical 
energy. Any one form of energy may be changed into another 
form. We may observe such a change when we strike a nail with 
a hammer and discover that the nail becomes hot. Our mechani- 
cal energy has turned into heat energy. 

Demonstration 1. Show some elements, as carbon, iron, phosphorus, 
and sulphur. 



24 



THE WORLD WE LIVE IX 



Forms of matter. Both living and non-living things are made 
up of chemical elements. There are over ninety elements. The 

common ones that are found in 
a tree are oxygen, carbon, nitro- 
gen, and hydrogen ; while a 
number of others, less com- 
mon, such as sulphur, potas- 
fsiuru, iron, and phosphorus, 
^^""^j 1 are also found in the composi- 

\j tion of most plants and ani- 
cacyo&n 76% I ma l s - Many of these same 

elements are found in soil, in 
air, and in water. Some ele- 
ments are gases, such as oxygen 
and nitrogen. Some are solids, 
such as carbon and sulphur, 
and two which are not found 
in the composition of the tree 
are liquids, mercury and bromine. Elements are simple substances. 
For example, iron, so far as we know, has nothing but iron in it : 
and oxygen nothing but oxygen in it. It is easy to separate some 
elements from their compounds and not so easy to get others. 
Carbon, for example, in its pure state is obtained when we collect 
on a sheet of white paper the black substance from the smoke 
of a candle. Soot is almost pure carbon. The yellow sulphur that 
we buy at the drug store is an element. It is not so easy to 
obtain oxygen in a pure state. This element is often combined 
in nature with other elements to form substances called com- 
pounds. A simple compound containing oxygen is water. 




The percentage of different chemical elements 
that are found in the human body. How do you 

account for such a large proportion of the gas 
oxygen? 



Demonstration 2. The separation of water into its elements. If 
by means of the apparatus shown in the diagram an electric current 
is passed through water to which a little sulphuric acid has been added, 
we find that the water separates into two gases. In one tube the gas 
present occupies just half as much space as in the other tube. The 
gas present in the smaller quantity proves upon test to be oxygen 
as it causes a glowing splinter to burst into flame. The other gas. color- 
less, tasteless, and odorless like the oxygen, differs from it by igniting 
with a slight explosion when a burning match or splinter is introduced 



OXYGEN 



25 



into the tube. As the gas burns, drops of water are formed, showing 
that it is passing back to its original condition, that is, it is uniting 
with oxygen to form water. This gas is hydrogen. Elements always 
unite in definite proportions to 
form compounds, as in water the 
proportion by volume is always 
two parts of hydrogen to one 
part of oxygen. 

Oxygen, when carefully pre- 
pared, is found to be colorless, 
odorless, and tasteless. Com- 
bined with other substances, it 
forms a very large part of the 
composition of water, rocks, 
minerals, and the bodies of 
plants and animals. 

Oxygen has the very important property of uniting with many 
other substances. The chemical union of oxygen with another 
substance is called oxidation. When a candle burns, the oxygen 
in the air unites with the carbon in the candle and forms a gas, 
called carbon dioxide, which puts out a flame. This gas may be 
tested for as follows : 

Demonstration 3. Burn a candle in a closed jar. After the candle 
goes out, remove it carefully (the gas in the jar is heavier than air). 
Add a spoonful of limewater — screw down the top of the jar and shake 





carbon dioxiote, 
Cafborx ccnd 
^^cter- vetpor- 
in the srnoks 



lisht^ and. 

I b&b energy 



ccr-bon 



Why is the burning of a match an example of 
oxidation ? 



so as to mix the gas in the jar 
with the limewater. What hap- 
pens to the limewater ? This test 
with limewater shows that carbon 
has been oxidized, forming carbon 
dioxide. 

Practical Exercise 1. Burn a 
number of different substances in 
closed jars and test in each case for 
carbon dioxide. How many of the 
substances produce carbon dioxide 
when burned ? 

Oxidation. Oxidation may 
take place slowly, as in the 
rusting of an iron nail, which 
is caused by oxygen uniting 



26 



THE WORLD WE LIVE IN 



with the element iron. Slow oxidation of chemical compounds is 
constantly taking place in nature and is a part of the process of de- 
cay and of breaking down of complex materials into simpler forms. 
One of the most important effects of oxidation lies in the fact 
that, when anything is oxidized, heat is produced. This heat 
may be of the greatest use. Coal, in being oxidized, gives off 

heat; this heat boils 
the water in the tubes 
of a boiler; steam is 
generated, wheels of 
an engine are turned, 
and work is performed. 
The energy released by 
the burning of coal 
has been transformed 
into work or power. 
We shall find later 
that the oxidation of 
certain materials in 
the bodies of plants 
or animals releases 
energy which is used 
to perform work. 
The heat of the hu- 
man body is main- 
tained by the constant 
slow oxidation of food 
materials within the 
body. 

Forms of energy. Energy has been shown to be the power to 
do work. The energy locked in the coal before it is released by 
the process of burning is known as potential or stored energy. 
The energy released by the burning process is kinetic or active 
energy. The potential energy held in the water of the San 
Francisquito dam became kinetic energy when the dam gave way 
and let the great volume of water rush down the fertile Santa 
Clara valley, bringing death and destruction to its inhabitants. 




Engineering News-Record 

The energy held in the water in this dam was sufficient to 
uproot trees, sweep buildings from their foundations, and 
dislodge rocks, when a wall of the dam broke. 



COMPOSITION OF LIVING THINGS 27 

Conservation of energy. Physical science teaches us that 
energy, such as that released so disastrously in that California 
valley, may never be lost, created, or destroyed. It always is, 
and always has been. The great force, released when the flood 
rushed down the valley, dug deep channels in the soil, moved huge 
rocks, smashed houses, and left countless other ruins in its ruthless 
path. If the water could have been harnessed to a turbine, it 
might have turned a dynamo, produced electricity, lighted a city, 
or turned the wheels of factories. Energy may be changed from 
one form to another, but it can never be created or destroyed ; it 
is everlasting ! 

Practical Exercise 2. Give three examples of transformation of energy that 
helps to make life more comfortable for you. 

Water in living things. Water forms an important part of the 
substance of plants and animals. This is seen when a number of 
green leaves are weighed, placed in a hot oven for a few moments, 
and then re weighed. The same experiment made with a soft- 
bodied animal, as the oyster, would show the presence of a greater 
percentage of water than was found in leaves. Some jellyfish 
are over 90 per cent water. Over 65 per cent of the human body 
is water. 

Mineral matter in living things. If a piece of wood is burned 
in a very hot fire, the carbon in it will all be consumed, and even- 
tually nothing will be left except a grayish ash. This ash consists 
of mineral matter which the plant has taken up from the soil dis- 
solved in water, and which has been stored in the wood or leaves. 
All living things contain small quantities of mineral substances. 

Practical Exercise 3. Weigh several different substances such as soil, apple, 
meat, dried beans, celery, etc. Dry out each substance in an oven under slow 
heat (do not char) . After several hours reweigh and determine percentages of 
water lost by each substance. Then try to burn out all organic material. 
The gray residue is the ash or mineral content. What per cent of the orig- 
inal weight is the ash? 

Gases present in living things. Some gases are found in a free 
state in the bodies of plants or animals. Oxygen is of course 
present wherever oxidation of organic matter is taking place, as is 
carbon dioxide. Other gases may be present in minute quantities. 



28 THE WORLD WE LIVE IN 

Materials found in tree. Our experiments have shown us that 
elements may be separated from compounds, and elements may be 
built up into compounds. In a living tree similar processes are con- 
tinually going on. Compounds containing the elements sulphur, 
potassium, iron, etc., are taken from the earth, dissolved in water. 
Nitrogen, which is an absolute necessity for building living 
material, is taken from the earth in the form of very complicated 
compounds which usually come from the decaying bodies of plants 
and animals and are found in the black soil we call humus. Oxygen 
comes from the air and is taken into the plant through breathing 
holes in the leaves. All together, the tree is a wonderful laboratory, 
for out of these raw materials it builds foods and from these foods 
it builds its own wonderful structure. The leaves not only make 
food in the sunlight, but they digest and circulate it to all parts 
of the plant. This may be done in darkness as well as in light. 

The table on the opposite page gives us the characteristics of 
the most common elements that are found in the tree and its en- 
vironment. It will also tell us how to identify each of these ele- 
ments by testing for those properties by which they are known, 
where they are found, and what use they have in nature. 

Self-Testing Exercise 

Matter is anything that has (1) or occupies (2). 

It may be in the form of a (3), a (4), or a (5). 

Energy is (6) to do (7). One form of energy may be 

(8) into another, as is seen in making (9) by means of 

water power. Energy may be stored in a substance as (10) 

energy, but when released to do work, it is (11) energy. 

Both (12) and (13) things are made up of 

(14) elements. There are over (15) in all. The commonest 

ones found in living things are (16), (17), 

(18), and (19). Elements combine in (20) propor- 
tions to form (21), as two parts of (22) and one 

part of (23) form water. When anything (24) with 

oxygen, we say (25) is taking place. If an organic substance 

is (26) or oxidized, it gives off (27) (28). 

If (29) turns (30), when used as a test for this gas we 

know that ........ (31) (32) is present, 



MATERIALS FOUND IN LIVING THINGS 



29 







o o 

X P 

2 s 

p p 



11 

p cr 



S-" 

3- 

o 



H O 

S° -p- P- 

cd P t-i 



- CD ^ 

cr p- &2 

p 3- 

5. p- 
p p 

ffq n 

P - 

cd 

p 



<! ^ P 

&§ J 

o 



p p 

P o 
p 



g >d 

p ct> 

P 3 

^p 

CD CD 
P- P- 




£ CD 

HJ SO 



^ 









I £ 



* 3 
i^. p 

CO X 



cd yi- 



Q 

p CO 
CO I 

CD I 



o 



CD c-t- O 

CP P-S, 



00 



ro 



II 

CO 

a* 

P 



CD -T 5 



- P 
^ P 

p cr 



0q 

co cr 

P <*■ 

Sj CD 



CD 

co >-; 

P.i° cT 

P ^ hL 

(R 2 ^ 

on & « 

CT e+ 

B CD 

P co 



O oo I 

fro ' 

p " 2f 

L~ <J CD 

CT CD £0 

3 

CO [— . 

0q" O 

B- Q- 

e-t- O 



o 
° § g 7 

p^ £ I 

2 P CD o 
P O CO o 





rw 




o 


s| 




p 


p- 


r-f- 




a> 




<-i 


1 




cr 


p 


p 






CD 


pr 



CD 



CD 



1*8. 

<r*- CD O 

B- P is 

P'&^ 



CD 

CO b 
GO 

cr 



W 



CD 



si l- 

►§ EL » EL 
p- £ 

P C5 



CO ^ 

o >r 

p - 

CD co 

~ O 

CD CH 



►P .h 



s i 

cr o 
o b 

CD Q_, 



o 

CD B 

0q >P 

co O 

P 



o 

<W (jq 

3 § 
>p p. 



CD 



3 g 

§ S 
p- 

2. ° 
o EL 



O W CD 

o f= p 

1« 

P- cr 

'p o - 
go ^ 



521 

S o ^ 

CL O CO 

=*• co 

cr o p 

B $"< 
CD co 

p 

CD O 



2^ 5 



O 

M. O 

s 3 
?l 

O CD 

g&- 

a EL 



a 



pi^p < 

<j O CD 

cw g,P 

3 ^ §■" 

P P* o 
2 p aq 

» S 3 

p o 

3 3 



SI 



p 

c-t- 
CD 

p 

pi *< 

p 
p 



CD 

§ g. 

CD CD £+ 

co p 5 

» s s 

3 5S " 

§ S o 



^.p 

3 CP 
Qfq 
B P 

3 p 

P c-^ 

<*- p. 
2 p 



30 THE WORLD WE LIVE IN 

PROBLEM m. WHAT ARE FOODS AND HOW ARE THEY 

USED? 

Foods. What is a food? We know that if we eat a suitable 
amount of proper foods at regular times, we shall be able to go on 
doing a certain amount of work, both physical and mental. We 
know, too, that day by day, if our general health is good, we may 
be adding weight to our bodies, and that added weight comes as 
the result of eating food. A similar statement may be made with 
reference to plants and foods. If food is supplied in proper quan- 
tity and proportion, plants will live and grow ; if their food sup- 
ply is cut off, or even greatly reduced, they will suffer and may die. 




-f 



-muscle — . nutrient. 
tendon) \foo<£ 

Tboixe* J 



Compare this turkey leg with other materials used as food, by making similar analysis of them. 

However, only a small part of a food, as potatoes, can be used 
by the body. For a food is made up of a combination of wastes — 
as water in vegetables, skins of fruits, and tendons in meat — 
and nutrients which repair or build up the body or, when oxidized in 
the body, furnish it with energy. The organic nutrients found in 
foods are carbohydrates, fats or oils, and proteins. 

Carbohydrates. Starch and sugar are common examples of 
this group of substances. The former we find in our cereals and 
most of our vegetables. Several kinds of sugar, such as cane 
sugar, beet sugar, and glucose or grape sugar, are commonly used 
as food. Glucose, the natural sugar of grapes, honey, and fruits, 
is manufactured commercially from starch by the action of dilute 
acids. It is used as an adulterant in sirups, honey, and candy. 



FOODS 31 

Fats and oils. Fats and oils form a part of the composition 
of plants and animals. Examples of food containing fat are : 
butter and cream, oils from nuts and olives, and fat from animals. 

Proteins. Proteins contain the element nitrogen in addition 
to carbon, hydrogen, and oxygen of the carbohydrates and fats 
and oils. They include some of the most complex substances 
known to the chemist, and, as we shall see, have a chemical com- 
position very similar to that of living matter. Proteins occur in 
different substances. White of egg, lean meat, beans, and peas 
are examples of substances composed largely of proteins. 

Vitamins. Vitamins, substances the composition of which is 
practically unknown as yet, are also necessary parts of a diet. 
We shall learn more about them in Unit XL 

Inorganic nutrients. Water and various salts, some of which, 
as calcium found in drinking water, form important parts of the 
diet of plants and animals. Later we shall see that green plants, 
although they use precisely the same nutrients (carbohydrates, 
oils, and proteins) as we do, take into their bodies the chemical ele- 
ments from which these are formed. From these raw food ma- 
terials organic foods are manufactured in the body of the plant. 

The tree. Foods in a fluid form are circulated to all parts of 
a tree. It grows by elongating its roots and its branches, and 
by putting on a thin layer of living matter on all parts of its body. 
This layer grows more in summer than in winter. If we 
should cut down a tree, we can see the concentric rings in its 
trunk which mark its yearly growth. How did the tree do this? 
Here again the chemical laboratory is at work. The organic 
foods which were made consist of the same elements that are 
found in the living stuff of the tree. These foods were used, not 
only to supply energy so that the tree may do work, but they 
give it the materials out of which to build its living material. 

Self-Testixg Exercise 

A nutrient is anything that supplies (1\ and (2) or 

(3) up the (4) of living things. Foods are made up of 

(o) and (6). The organic nutrients are (7) , 

:' (8) or (9), and (10). 



32 



THE WORLD WE LIVE IN 



PROBLEM IV. HOW DOES MAN CONTROL HIS 
ENVIRONMENT? 

Natural environment. Besides the chemical elements in our 
surroundings, temperature, absence or presence of water, the kind 
of earth surface, the presence of different salts in the soil or water, 
all may play a part in determining what kind of life will be 
present in a given locality. Mountain, plain, desert, lake, woods, 
tropical jungle, each has its own inhabitants and these inhabitants 
are limited to life in that particular part of the world. 




Photo by Doaglas-Xesmlth & Associates 
A city apartment house. Why do we consider this a favorable artificial environment ? 

Man, while he is like other animals in requiring heat, light, 
water, and food, differs from them in that he has come to live in a 
more or less artificial environment. Men who lived on the earth 
thousands of years ago did not wear clothes or have elaborate 
homes of wood, brick, or stone. They did not use fire, nor did they 
eat cooked foods. But, by slow degrees, man has come to live in 
an environment changed from that of other animals. He has 
learned to build houses and to use fire. The living together of 
men in communities has caused certain needs to develop. Many 
things can be supplied in common, as water, milk, and fuel. Wastes 



NATURAL ENVIRONMENT 



33 



of all kinds in a town or city have to be disposed of. Homes are 
now placed close together, or built one on top of another, as in 
modern apartment buildings. Fields and trees, in fact most 
aspects of country outdoor life, have virtually disappeared in a 
large city. City-dwelling man has come to live in an artificial 
environment. 

Care and improvement of the environment. Man can modify 
or change his surroundings by making this artificial environment 
favorable to live in. He can heat his dwellings in winter and cool 




Why do we call this an unfavorable natural environment ? 



Wright Pierce 



them in summer so as to maintain a moderate and nearly con- 
stant temperature. He can have windows in his dwellings to 
let light and air pass in and out. He can have light at night and 
shade from intense light by day. He can have pure water in his 
home, and drains or sewers to carry away his wastes. He can 
plan parks and playgrounds so that the city people may have 
breathing spaces, as do people in the smaller towns. He can see 
to it that people ill with communicable diseases are isolated 01 
quarantined from others. Best of all, he is slowly learning to con- 
trol the tiny parasites, plant and animal, that cause and spread 



34 THE WORLD WE LIVE IN 

diseases. This care of the artificial environment is known as 
sanitation, while the care of the individual for himself is known 
as hygiene. 

Self-Testing Exercise 

The environment is our (1). With man much of this en- 
vironment is (2) . He can (3) his environment while 

other living things (4) do this. The (5) of the 

artificial environment is called (6), the care of the individual 

for himself without considering his (7) is (8) . 

Organization of work. In each unit there are certain funda- 
mental things that we must learn and do. Everything in a unit 
is not of equal importance. It, therefore, is necessary for you to 
decide on the most important material from which you will make 
your recitation. To make this organization, a summary outline 
which you can use as a guide is helpful, as : 

The tree a living thing Energy — forms of 

What does it use in its environment? Conservation of 

How does it get it ? Foods and nutrients 

Matter — what is it ? Kinds of each 

Elements and compounds Control of environment by man 
Oxygen and oxidation 
Elements found in living things 

In all except the first two or three units, there will be no sum- 
mary outline and you will be expected to make one for your note- 
book. You should also test your knowledge of the unit in the 
following ways : (1) answer and check all of the survey questions ; 
(2) perform all assigned exercises or laboratory work ; and (3) check 
with your teacher the various self-testing exercises, including the 
final test on fundamental concepts and the attainment test. 

Test on Fundamental Concepts 

Make in your notebook two vertical columns, one headed CORRECT and the other 
INCORRECT. In the first column place the number of the statements you think are right, in 
the second the ones you think are wrong. Your grade = number right X 4. 

I. The environment (1) contains the same chemical elements as do 
the living things in it ; (2) has the same chemical composition as living 
things ; (3) is everything that surrounds us ; (4) can be controlled by 
man ; (5) determines the kind of plants or animals living in it. 



TESTS 35 

II. Matter (61 is anything that has weight; (7) is easily destroyed : 
(8) is material in the form of gas, liquid, or solid ; (9) can be changed 
from one form to another: (10) is organic or inorganic. 

III. Energy (11) can be either gaseous or liquid ; (12) is power to do 
work : (13.) may be released by oxidation ; (14) is potential or kinetic : 
(15 ) is stored in the foods we eat. 

IV. Foods (16) contain waste material; (17) are all obtained in 
their final state from the soil ; (18) contain nutrients ; (19) are used 
by plants and animals to release energy and to build and repair tis- 
sue; (20) are made by green plants. 

V. Man (21) can control his environment : (22) needs green plants 
to make food; (23) is not able to oxidize food to release energy; 

24 is composed of the same chemical elements as his environment; 
(25 is the only living thing that can change his environment. 

Achievement Test 

1. How can you make oxygen? 

2. How do you test for carbon dioxide ? 

3. What chemical and physical happenings take place when you 
burn a match? 

■1. What are the chemist's symbols for oxygen, nitrogen, carbon. 
hydrogen, and carbon dioxide? 

5. What is meant by the term " conservation of energy '"? How 
could you perform a demonstration to prove it ? 

6. How can you distinguish between the natural and artificial 
factors of your environment ? 

Practical Problems 

1. List the ways in which a tree and man use their environments. 
List the natural and artificial factors of your environment. 

2. Take some factor of the environment in your community that 
you think is poor and make definite suggestions for its improvement. 

3. Show some example of conservation of energy taken from your 
own home environment; from the country in which you live. 

L'sefct References 

Downing. Our Living World, pp. 309-350. (Longmans, Green. & Co.. 
New York. 1924.) 

Hunter, G. W.. and Whitman. W. G.. Problems in General Science. 
14 Control of Environment.''' pp. 15-34. (American Book Company.) 

Pack, Trees as Good Citizens, pp. 17-26. (American Tree Associa- 
tion, Washington, D.C., 1922.) 




SURVEY QUESTIONS 

What do we mean by "being alive"? Why do plants and animals 
turn toward or away from the source of light ? Are they affected by other 
factors of their environment ? Could you name some things that all living 
things can do ? What is meant by the term " adaptation " ? 



UNIT II 



WHAT IS BEING ALIVE? THE FUNCTIONS OF LIVING 

THINGS 

Preview. We have seen in our study of elementary science, 
several differences between living and non-living matter. Water, 
for example, when cooled sufficiently, becomes ice, or, if heated 
to the boiling point, becomes vapor. In order to be changed it 
has to be acted upon by outside forces. But when a plant or an 
animal grows, or moves, or in some other way manifests energy, 
that energy is released by the living thing itself. 

We think of things as being alive when they do something. Yet 
water may turn a wheel and generate electricity which has a force 
capable of " doing something." Such a force may set off a blast 

36 



PREVIEW 37 

of dynamite. Or electricity, in the form of a flash of lightning, 
may destroy a tree. 

It is not easy to tell exactly what it is to be alive, any more than 
it is easy to tell what electricity is or what radioactivity is. Elec- 
tricity is a servant of man, but the greatest expert cannot tell 
what the force actually is. Life is a manifestation of forces, like 
a flame or electricity. Every living thing, as we shall see later, 
is like a steam engine or any other machine, in that it is a medium 
used for the transformation of energy. So to understand the 
meaning of life we had better start by trying to see how living 
things act in their normal environment when outside forces influ- 
ence them. 

One of the world's great biologists, Jacques Loeb (zhak lob), 
some years before his death attempted to prove that all living 
things are more or less automatically controlled by the factors 
of their environment. He assumed that all living matter is sensi- 
tive and that it responds or reacts to the forces of its environment, 
in very definite ways. These forces we call stimuli (sing, stimulus) ; 
the response which is made to such a stimulus we call a tropism. 
Loeb and his followers have shown quite conclusively that living 
matter responds very definitely to temperature, touch, chemical 
substances, electricity, and various other factors of the environ- 
ment. The behavior of plants and animals in response to these 
various stimuli is one indication of being alive. 

Response to stimuli is evidenced by activity or movement. 
Movement in living things is brought about by changes within 
the living material of which the organism is composed, while the 
movement of non-living things, as an engine, is brought about by 
the force of burning coal or exploding gasoline. This activity 
is due to the fact that living things are like engines in another 
respect : while the engine oxidizes fuel to release energy, they 
oxidize the food taken into their bodies and release energy in the 
form of motion or other kinds of work. 

Any living thing, plant or animal, must get food and digest it, 

must circulate this digested food to various parts of its body, must 

assimilate or make the prepared food into a part of itself, must 

excrete or get rid of wastes, and must reproduce or form new 

h. bio — 4 



38 



WHAT IS BEING ALIVE? 



plants or animals. Adaptability is also a characteristic of living 
things. We say that a plant or animal adapts itself to its sur- 
roundings, meaning that some structure of the animal or plant 
has made it possible for the organism to live under the conditions 
in which it is placed. 

A little over two hundred years ago, a Dutchman, Anton van 
Leeuwenhoek (la'ven-hdok), became interested in lenses. He 





observer 



Culver Service 



Anton van Leeuwenhoek was at first 
only interested in grinding lenses and mak- 
ing crude microscopes so that he could 
see things Digger than the naked eye 
could see them. But later he became in- 
terested in observing minute animals that 
could not be seen with the naked eye. 
Through his discoveries and observation, 
incentive was given to the study of bac- 
teria. 



ground hundreds of them, and used them in various combinations 
to magnify tiny plants and animals. With these improved lenses 
he was able to see tiny organisms swimming in drops of pond water, 
and it is even thought that he probably saw living bacteria. An 
English doctor, Robert Hooke (1635-1703), examined a small section 
of Cork, which is the bark of an oak tree, and found it was made up 
of tiny compartments, like rooms, which he called cells, a term which 
is now universally used for the unit of structure in living things. 



STIMULI 39 

The name cell is not very descriptive. Hooke saw the dead walls 
around the spaces that during the life of the plant contained living 
matter. But it was not until more recent times that biologists 
found that the contents of the cell is the important living sub- 
stance. This living material has been named protoplasm (Gr. 
protos, first; plasma, formative material). While we rarely see 
it or feel it, nevertheless observation has shown it to be always 
present where there is life. It is a sticky, semi-fluid substance, 
somewhat like the white of an egg in consistency. Its chemical 
composition is very difficult to discover and it is probable that 
there are a number of different kinds of protoplasms in the bodies 
of plants and animals. Under the microscope it seems to be either 
granular, or made of tiny bubbles floating in a more fluid medium, 
or it sometimes appears to be made up of delicate fibers or threads, 
forming a network of infinite complexity. The cell is always found 
in the structure of living things, just as bricks make up the structure 
of a wall or a house. 

PROBLEM I. WHAT DO WE MEAN BY REACTION TO 
STIMULI? 

Demonstrations. 1. Reaction to water. Plant some bean seeds 
in sawdust in a box with glass front. Water the seeds in one end of 
the box only. How do the roots grow? 

2. Reaction to light. Put oxalis or other plant in a place where it 
will receive light on one side only. Put some earthworms in a pan 
covered at one end. What happens in each case? 

3. Reaction to gravity. Place a pocket garden (see page 142), in 
which radish seeds are germinating, on end and then turn it two or 
three times at intervals of 24 hours. What happens? 

4. Reaction to chemical stimuli. Make observations on young 
seedlings growing in solutions containing a lack of certain chemical 
elements necessary for growth (see page 609) . What do you find ? 

5. Reaction to temperature. Put some beans in moist sawdust in 
vessels. Put one vessel in the ice-box, another in a moderately warm 
room, and the third in an oven where the temperature is over 160° F. 
Observe what happens. 

Water. It is a well-known fact that living things need water, 
in order to sustain life. The roots of green plants grow toward a 
source of water. Some animals appear to be stimulated to move 
toward water, whereas others move away from moisture. Water 
is of so much importance to man that from the time of the Caesars 



40 



WHAT IS BEING ALIVE? 



until now he has spent enormous sums of money to bring pure 
water to his cities. 




U. S. Forest Service 
An irrigated ranch. Why is the vegetation unusually thick along the water edge ? 

Light. Light is another important factor of the environment. 
A study of the leaves on any green plant growing near a window 
will convince one that the stems of such plants grow toward the 
light, and that the leaves grow in positions to get a maximum 
amount of sunlight. All green plants are thus influenced by the 
sun. We say an organism is positively influenced by a stimulus 
when it turns or moves toward that stimulus, and that it is nega- 
tively responsive when it turns or moves away from the stimulus. 
Other plants which are not green seem either indifferent or nega- 
tively influenced by the stimulus of light. The direction, as well 
as the intensity of light, is an important factor. Animals may or 
may not be attracted by light. A moth, for example, will fly 
toward a flame ; an earthworm will move away from light. Some 
animals prefer a moderate or weak intensity of light and live in 
shady forests or jungles, prowling about at night. Others seem 
to need strong light. Man himself is most comfortable and works 
most efficiently in a moderate intensity of light. 



TROPISMS 



41 



Gravity. Another factor influencing both plants and animals 
is gravity. The main or top roots of plants, for example, tend to 
grow downward. Lateral roots, on the other hand, grow in an 
approximately horizontal direction. Careful experiments in 
which other forces are substituted for the pull of gravity have 
proven that gravity is the attractive force. The stem, on the 
other hand, grows upward. This seems to be a negative response 
to gravity. Many animals show this response to gravity in very 
definite ways. The maintenance of one's equilibrium is un- 
doubtedly a response to gravity, as has been proved in some of 
the lower animals, such as shrimps and fishes. 

Food or chemical substances. Plants are greatly influenced by 
the presence or absence of chemical substances in the soil. You 
have probably noticed the differences between plants that grow near 
the sea, where salt is found in the soil, and those growing inland. 
No one who has traveled in a country where the soil is impregnated 
with alkali can fail to see the differences between vegetation there 




How does the seedling show energy ? How does the man ? 

and in other regions where no alkali exists but where similar condi- 
tions of temperature and moisture are found. Since the mineral 
salts of the soil are absorbed by the plant and later built into it, we 
can easily see that responses of this sort are of the utmost importance. 
Temperature. Living things are affected by heat or cold. 
Animals and small plants that are able to move in the water fre- 



42 WHAT IS BEING ALIVE? 

quently go away from a temperature that becomes unfavorable 
to their existence. In cold weather, green plants either die or 
temporarily suspend their life activities. They become dormant. 
Likewise, small animals, such as insects, which might be killed 
by cold, usually hibernate under stones or boards. Their life 
activities are slowed down until the coming of warm weather. 
Bears and some other large animals go to sleep during the winter 
and awake, thin and hungry, on the approach of warm weather. 
Animals and plants used to certain temperatures frequently die if 
they are put in a colder or hotter climate. Even man, one of the 
most adaptable of all animals, cannot stand great changes without 
discomfort and sometimes death. He heats his houses in winter 
and sometimes cools them in summer, so as to have the amount 
of heat most favorable to his health ; namely, about 68° Fahrenheit. 
The value of tropisms. A study of hundreds of experiments 
with plants and animals shows us that their instinctive responses or 
tropisms are of the greatest use to them. Response to a favorable 
stimulus results in placing the living plant or animal where it can get 
food, light, or more moisture and thus better succeed in the world. 
In general, tropisms bring the plants or animals into adjustment 
with their environment so that they may obtain what they need in 
order to succeed in the surroundings in which they must live. 

Practical Exercise. Make a list of as many responses to stimuli in the plant 
world as you can find and classify them under the headings given above. Do 
the same thing for animals. Then make a list of your own responses and 
classify them in the same manner. Do you differ markedly in your responses 
from plants? From lower animals? If so, how? 

Self-Testing Exercise 

Tropisms are the (1) (2) of plants and animals to 

certain (3) in their (4) . Roots of plants react 

(5) to gravity while the stems react (6). Roots grow 

toward (7), and leaves usually turn toward the (8). 

Earthworms will move (9) the light. Tropisms help bring plants 

and animals into (10) with their (11), so that they 

can (12) there. Plants are affected by the (13) 

(14) found in the soil. Living things are affected by 

(15) and (16). 



SENSATION AND MOTION 



43 



PROBLEM II. HOW ARE LIVING THINGS ALIKE AND HOW 
DO THEY DIFFER? 

Laboratory Exercise. Compare a living plant and a living animal, 
with reference to life functions. Use living grasshoppers under glass tum- 
blers placed over a bean seedling, a small living weed or a grass plant. 
Use the text of the problem which follows as a laboratory guide. 

If we attempt to compare an insect with the plant on which 
it feeds, we see several points of likeness and difference at once. 
Both plant and insect are made up of parts, each of which, as the 
stem of the plant or the leg of the insect, appears to be distinct, but 
which is a part of the whole living plant or animal. Each part of 
the living plant or animal which has a separate work to do is called 
an organ. Plants and animals, therefore, are spoken of as organisms. 




Read your text carefully and compare the uses of the parts of the plant 
and the insect given in the diagram. 

In spite of the apparent differences between a green plant, such 
as a tree, and an animal, like the grasshopper, the life functions 
or processes are very similar, as we shall see in the paragraphs that 
follow. 

Sensation and motion. We have already shown that all living 
things respond to various stimuli. The stem of a green plant 
turns toward the light, an earthworm shuns the sun's rays. Plants, 
as well as animals, move, as is observed in the movements of roots 
toward a source of water, or the movements of fish in a stream 
so that they head up against the current. 



44 



WHAT IS BEIXG ALIVE? 




..root- hairs 



In what ways are the circulations of a plant and an animal alike ? tained 
In what ways do they differ? 



Food taking. It is not so easy to prove at this time that all living 
things take food. We know animals will die without a food 

supply. We also 
know that some 
plants, like molds 
or mildews, grow 
on food substances. 
But green plants 
live in soil appar- 
ently without food 
if they have a niod- 
1 Xs & erate water supply. 
This is possible be- 
cause green plants 
make organic food 
substances out of 
the materials ob- 
from the 
soil, of water, and 
a part of the air. Both plants and animals use organic food sub- 
stances in exactly the same way, that is, they get energy out of 
them to do work, and they build up their bodily material out of 
the food they use. 

Respiration. Respiration is the process by which oxygen is 
supplied to the body and carbon dioxide is removed. As a result 
food is oxidized and energy is released. The processes are the 
same in both plants and animals as will be shown in detail later. 
Plants release enough energy to force then way through the 
compact earth: animals release their energy in the activity we 
associate with running, swimming, flying, etc. 

Nutrition. The foods of plants and animals must be made 
liquid so that they may pass freely to various parts of the organism 
to be used there. In order to do this they must be digested, or 
changed to a form that will enable it to be taken in by the smallest 
units of body structure, the cells. The way this is done will form 
the basis of an important problem later on in our course. Then 
these foods must be absorbed or taken into the organs of circulation. 



FUNCTIONS OF LIVING THINGS 



45 



which are woody tubes in plants and blood vessels in animals. 
Then this digested food must finally become part of the living 
organism by assimilation. 

Excretion. Wastes, such as water, carbon dioxide, and urea, are 
formed in the body by oxidation and other changes. If these wastes 
are not eliminated at once, they interfere with the normal working 
of the body. Therefore excretion is a necessary body function. 

Reproduction. Reproduction, or the formation of new organisms, 
is the outcome of all the nutritive processes. Plants and animals 
have various methods of giving rise to new plants and animals. 
But the result is the same in both cases ; that mysterious something 
we call life is started again as a seed, an egg, or a baby animal to 
become in time a parent of another generation of life. Some of 
the material in the following units deal with this life function. 

Practical Exercise. List for comparison the evidences of life processes (men- 
tioned in preceding paragraphs) in a common plant and in an animal. 



1 ■ *• . '- 




Or '^^^^ 


§;\ %' 







H. Armstrong Roberts 
Animals and plants give rise to new organisms. These offspring resemble their parents and 
each other. Yet, very seldom do we find two individuals exactly alike. 



Self-Testing Exercise 

.Living things, because they are (1) of (2) are called 

organisms. Both plants and animals have similar (3). 



46 



WHAT IS BEING ALIVE? 



They both respond to (4), use (5) to grow or release 

(6), and respire. Nutrition is the process by which living 

things (8), (9), (10) and (11) food. 



jauc)eu5 






vacuole 



PROBLEM III. WHAT ARE CELLS AND HOW DO THEY 
PRODUCE OTHERS? 

Laboratory Exercise. Put a drop of impure water on a slide. Cover 
with a cover slide and observe it under a compound microscope. Adjust 
the lenses until the particles in the water can be plainly seen. 

Now scrape, with a sterilized toothpick, the inside of the cheek. Place 
a small bit of the material in a drop of pure water on a glass slide and 

stain it with a small drop of 
diluted fountain pen ink or 
methylene blue. Notice the 
irregular blue structures or 
cells. Find a deeper blue body 
inside the cell. This is the 
n ucleus. The outer faint blue 
line marking the edge of the 
cell is the cell membrane. 

Peel the skin from one of 
the fleshy leaves forming an 
onion bulb, mount a small bit 
of it in water to which is 
added a drop of dilute tinc- 
ture of iodine. Examine it 
under a microscope. Note 
the cells. Plant cells differ 
Chloroplast from animal cells in that they 
have a delicate wood icall out- 
side the membrane. Draw 
two or three animal and plant 
cells in your notebook . Make 
each cell at least one inch in 
diameter. Label all parts. 

An examination of the delicate leaves of the Elodea, a water 
plant used in aquariums, shows cells with many large spaces or 
vacuoles, which are filled with a non-living fluid instead of proto- 
plasm. Forming a part of the protoplasm are many small ovoid 
bodies, most of which are green in color. These are the chloroplasts 
(klo'rfi-plasts) or chlorophyll (klo'rfi-fil) bodies (Gr. chloros, green ; 
phyllon, leaf). We shall see later that they are of the utmost im- 
portance to each one of us, as it is by means of the action of the sun 
upon them that food is manufactured in the green parts of plants. 




-ytoptem 



What are the characteristics of a plant cell? 
does Elodea differ from animal cells? 



How 



TISSUES AND ORGANS 



47 




M 

^-L - nucleus-. . -Tr^ 

...^excuote 

ceTl membrane- 



i) 



Onion cells and epithelial cells, 
these plant and animal cells alike ? 
they different? 



In what ways are 
In what wavs are 



In living Elodea, an interesting phenomenon may be observed. 

The protoplasm in the cell body is seen to be constantly in motion, 

flowing slowly in the direc- 
tion of the arrows shown 

in the diagram. This 

streaming of protoplasm is 

one of the manifestations 

of life within the cell. In 

many cells this movement 

may be observed, and we 

have reason to believe that 

the protoplasm in most 

living cells is in motion, 

thus affording a circulation 

of the cell contents. 
Tissues and organs. The 

cells which form certain 

parts of the veins, the flat 

blade, or other portions of a leaf, are found in groups or aggrega- 
tions, and are more or less alike in size and shape. Such a 

collection of cells is called a tissue. Examples of tissues in ani- 
mals are the cells 
covering the outside 
of the body, forming 
the skin or epidermal 
tissue ; muscle tis- 
sue, which produces 
movement; and 
bony tissue, winch 
forms the framework 
to which the muscles 
are attached. Tissue 
Explain ce Us often differ 
greatly in size and 

shape. A large plant or animal is ordinarily made up of more, 

not larger, cells than a smaller organism. 

Collections of tissues winch act together in the performance of 




Cells, tissues, and organs in plants and animals. 

this illustration. 



48 



WHAT IS BEING ALIVE? 



work form organs. Such an organ is a leaf, made of supporting 
cells, green cells, spongy cells, etc. : or the human arm, with its 
bony supporting tissue, its nerves and muscles, its blood vessels 
and connective tissue. 

How cells form others. Cells can grow only to a certain size. 
When this limit is reached, thccell splits, forming two ceUs. In 
this process, which is of very great importance in the growth of 
both plants and animals, the nucleus elongates and divides : the 
halves separate and go to opposite ends of the ceU. Then the rest 
of the protoplasm divides equally and two cells are formed, each 



f ~5f 



JU 



cc plant £€31 grows - cCivictes into t%e 



? 



hs 



c^ 




a white blood dhroVs - divides into two 
Cell & 

Plant and animal cells multiply by division. 

containing a nucleus. Each cell will have exactly the same char- 
acteristics possessed by the original cell. This process is known as 
direct cell division. Usually a more complicated process of division 
known as mitosis occurs in most cells. See diagram on page -i9. 

The chromosomes and their functions. If we now examine a 
specially prepared and stained cell,, for example,, the egg cell of a 
worm or a frog, we shall find that the nucleus, when stained with 
certain dyes, shows numerous small deeply stained bodies within 
it. These structures are called chromosomes (kro'mo-somz j 
Gr. chroma, color; soma, body), or color-bearing bodies. The 
number of these chromosomes in each body cell of a given kind of 
plant or animal is always the same. For example, forty-eight are 
found in man, four in a certain worm, and eight in one kind of lily. 
In plants and animals there are two distinct kinds of cells, one 
group called the somatic or body cells, which form the bulk of the 
body, and the sex cells which pass on the heredity qualities to the 
next generation. The sex cells are able to do this by means of 



CELL DIVISION 



49 



the chromosomes, which are believed to be the bearers of the 
hereditary qualities which can be handed down from parent to 
offspring. 





cell tfrows equatorial - 

and ctiviotes pi cxne^ 4. 



_ chromosomes; 

ST Splits anot _ 

travel to*&ret 

ypoles 





An animal cell showing mitotic division. During this division the chromatin granules form 
a coiled thread which finally breaks up into chromosomes. Each chromosome splits into two 
similar parts which go to the opposite ends of the cell, where they become a part of two 
new nuclei. At the same time a small structure, the centrosome, separates into two parts. A 
wall forms midway between the two nuclei, and the cell divides, forming two cells. 

Self-Testing Exercise 

Cells are the units of (1) of plants and animals. A plant 

cell differs from an animal cell by having a (2) (3) and 

containing (4). All cells contain a (5). Cells grow 

by (6) . Hereditary qualities are handed down from one 

generation to another by means of the (7) in the (8) 

(9). A collection of like cells is called a (10). 

An organ is made up of a (11) of (12) acting to- 
gether to do (13). 



PROBLEM IV. WHAT DO WE MEAN BY ADAPTATION? 

Demonstration 6. Show by means of charts, pictures, and actual 
examples, a number of adaptations such as bills and legs of birds ; wings 
of insects; teeth of carnivorous animals. Protective coloring in in- 
sects, and adaptations in plants, especially in cactus, pitcher plant, 



50 



WHAT IS BEING ALIVE? 




and thistle, are strik- 
ing examples. Op- 
portunity should be 
given for all members 
of the group to go, if 
possible, to a good 
museum where such 
material is on dis- 
play. 

Practical Exercise. 

List as many different 
examples of plant and 
animal adaptations as 
you can. Be prepared 
to explain them before 
the class. If possible, 
bring to class examples 
or diagrams of the 
animals or the plants 

Wright Pierce wMch ghow thege adap _ 
Mention several ways in which this cactus is fitted to live in tations 
the desert. 

Adaptability, a function of living things. Not only are plants 
and animals fitted to live under certain conditions, but each part 
of their bodies may be fitted to do certain work. I notice that as 
I write the fingers of my right hand grasp the pen firmly and the 
hand and arm execute some very complicated movements. This 

they are able to do 
because of the move- 
ment made possible 
by the arrangement 
of the delicate bones 
of the arm, a complex 
system of muscles 
which move the 
bones, and a direct- 
ing nervous system 
which plans the work. 
Because of the pe- 
culiar fitness in the 
structure of the hand 
for this work we say 
it is adapted to its 




Wright Pierce 



How does the beak of the eagle fit it for catching and using its 
food? 



ADAPTATIONS 



51 







PVf- « ^j 


r * 
Mr 




^■ki^L' ^ ■ SI 9 


fiS .^1 y 


yr' <l 


' '■ '1 


"^»Vt ' jpn^i 11(«J5 












'■Lm 


**M 


■ ^^V^^|v% 


5vL' ' 1 




i 









Wright Pierce 

How is this low plant with large succulent leaves fitted to live 
in a desert ? 



function of grasping 
objects. A structure 
which is useful to an 
organism in some 
special way is called 
an adaptation. 

Each part of a 
plant or animal is 
usually suited for 
some particular 
work. The root of 
a green plant, for 
example, is able to 
take in water by 
having tiny absorb- 
ing root hairs grow- 
ing from it. The stems have tubes to convey liquids up and 
down from roots to leaves, and are strong enough to support the 
leafy part of the plant. The thin, flat leaves are arranged to re- 
ceive a very large amount of sunlight and to act as solar engines, 
that is, using energy from the sun. Each part of a plant does 
work, and is fitted, 
by means of certain 
structures, to do that 
work. The lungs of 
a land animal are able 
to take oxygen from 
the air, while the gills 
of a fish can take their 
supply of oxygen 
only from the water ; 
that is, from the air 
that is dissolved in 
water. It is because 
of such adaptations 
that organisms are whom Pierce 

able to live Within What might be the advantages of a large flat leaf to a plant ? 




52 WHAT IS BEING ALIVE? 

their particular environments. Some adaptations are protective, 
as the bark of trees, the spines or thorns on some plants, the shells 
of turtles, the feathers of birds, the heavy hairy coats of a dog or 
a cat, the strong teeth of a tiger. The trunk of the elephant, the 
long neck of the giraffe, the pouch of the kangaroo, the flipper of 
the whale, or the web on the wing of the bat are all adaptations 
for various purposes. 

Practical Exercise. Classify the above adaptations according to their 
specific uses. Make a table giving at least five kinds of adaptations found 
in plants, and five kinds found in animals. 

Self-Testing Exercise 

An adaptation is a (1) that is (2) to an orgauism 

in some (3). By means of (4), (5) and 

(6) are enabled to (7) in various environments. 

Without adaptations (8) would be impossible. 

Review Summary 

Test your knowledge of the unit by : (1) Answering and rechecking the 
survey questions; (2) performing the assigned exercises; (3) checking with 
the teacher your scores on the various tests, and if you do not have a perfect 
score, try again the parts you missed ; (4) doing as much of the optional work 
as has been assigned to you ; and finally filling in the following outline as fully 
as possible for your notebook. 

Functions of living things Nutrition 

Reaction to stimuli Excretion 

water Reproduction 

light Cell unit of structure 
gravity parts 

chemical substances functions of 

temperatures formation of 

value of Adaptations 

Food taking of living things 

Respiration 

Test on Fundamental Concepts 

Make two columns on your notebook. Head one CORRECT, the other INCORRECT. 
Place in these columns the numbers of the sentences you think are right and those you think 
are wrong. Your grade will be the number correct X 4. 

I. Tropisms (1) are reactions to the various stimuli in the environ- 
ment; (2) are structures which cause reactions to stimuli; (3) make 
it possible for green plants to live without the sun ; (4) are brought 
about by food, water, light, heat, chemical substances, and other factors 
of the environment ; (5) bring the organism into adjustment with its 
environment. 



TESTS 53 

II. Both plants and animals (6) are made up of cells ; (7) react to 
stimuli ; (8) have the same life processes ; sensation, motion, respira- 
tion, nutrition, excretion, and reproduction ; (9) make food ; (10) re- 
lease energy from their food in order to do work. 

III. Cells (11) are made of living material ; (12) are always green in 
color; (13) all contain nuclei; (14) in both plants and animals are 
exactly alike ; (15) are units of building material in living things. 

IV. Growth in organisms takes place (16) by increase in the size of 
the cells ; (17) by increase in the number of the cells ; (18) by increase 
in the number of chromosomes in the cells ; (19) when cells composing 
them divide; (20) when the living matter takes in more food. 

V. A living thing (21) is adapted to live in a given environment when 
it has structures which fit it for that life ; (22) is adapted to do a given 
piece of work when it has structures that fit it for that work ; (23) may 
adapt itself to any environment ; (24) reacts to stimuli ; (25) will die 
if taken from its original environment. 

Achievement Test 

1. How do plants or animals react to stimuli? 

2. How would you perform at least one experiment to show tropism ? 

3. How can you distinguish between living and non-living things? 

4. Have you seen a cell? Name the parts and uses of each part. 

5. How can you make a classification of adaptations and show 
clearly just what you mean by this classification? 

Practical Problems 

1. Show specifically how man has made use of the fact that certain 
plants or animals react to the stimulus of light. 

2. Prove how some tropism is of value to a plant ; to an animal. 

3. Explain fully how your leg is adapted to its uses. 

Useful References 

Burlingame and others, General Biology. (Henry Holt & Co. 1928.) 
Caldwell, Skinner, Tietz, Biological Foundations of Education. (Ginn 

&Co. 1931.) 
Eikenberry and Waldron, Educational Biology. (Ginn & Co. 1930.) 
Loeb, Forced Movements, Tropisms and Animal Conduct. (J. B. 

Lippincott Co. 1918.) 
Plunkett, Outlines of Modern Biology. (Henry Holt & Co. 1930.) 
Shumway, General Biology. (John Wiley & Sons. 1931.) 
Thomson, The Outline of Science. (G. P. Putnam's Sons. 1922.) 
Transeau, General Botany. (World Book Company. 1923.) 
Wiggam, Fruit of the Family Tree. (Bobbs-Merrill Co. 1924.) 
h. bio — 5 




SURVEY QUESTIONS 

Do you think it is true that plants and animals depend on each other? 
Can you give any examples to prove this? Can you distinguish between 
full-grown and baby insects ? Do you know why insects are numerous ? 
Why do insects visit flowers ? Do you know why seeds are formed ? 



UNIT III 



HOW ARE ANIMALS AND PLANTS MUTUALLY 
DEPENDENT? 

Preview. Anyone who has been in the field cannot help thinking 
that insects have something to do with flowers and green plants. 
Grasshoppers eat the green leaves, beetles crawl over the golden- 
rods, butterflies light on flowers or deposit their eggs on some 
plant that their young will use as food. Almost everywhere honey- 
bees can be seen busily at work among the flowers. What are they 
all doing ? Is it something that we can discover for ourselves ? 

If we were to take a single tree for observation, we might find 
birds nesting in the branches ; perhaps a squirrel or two has a home 
there : insects of many kinds may be found on its leaves, or under 

54 



PREVIEW 55 

its bark ; while an examination of the soil around its roots would 
show us many other living forms such as the pupae and nymphs of 
insects. Perhaps our tree might have queer looking growths called 
galls on the leaves or stems. These, if examined, would be found 
to be the homes of tiny insects and bacteria. If the tree had 
flowers we should be sure to see numerous insects on them. 

Each insect has its own favorite food plant or plants, and in 
many cases the eggs are laid on the plant so that the young may 
have food close at hand. Some insects like the rotted wood of 
trees. An American zoologist, Packard, has listed 462 species 
of insects that live upon oak trees alone. Everywhere insects are 
engaged in taking their nourishment from plants, and millions of 
dollars of damage is done every year to gardens, fruits, and cereal 
crops by these animals. Insects in turn are the food of birds ; 
cats and dogs may kill birds ; lions and tigers live on large defense- 
less animals such as deer or cattle ; and finally, man eats the 
bodies of both plants and animals. But if we reduce this search 
for food to its final limit, we see that green plants provide all the 
food for animals. For the lion or tiger eats the deer which feeds 
upon grass or green shoots of young trees, and the cat eats the bird 
that fives on weed seeds or on insects that eat plants. Green 
plants supply the food of the world. 

On a field trip no one can fail to observe that plants often give 
animals a home. The grass shelters grasshoppers and smaller 
insects. Some insects, such as the tent caterpillar, build their 
homes in the trees or bushes on which they feed, while others 
tunnel through the wood, making homes there. Spiders build 
webs on plants, often using the leaves for shelter. Birds nest in 
trees, and many wild animals use the forest as their home. Man 
has learned to use many kinds of plant products to aid him in 
making his home, wood and various fibers being the most important 
of these products. 

So far it has seemed as if green plants benefited animals and 
received nothing in return. We shall see later that plants and 
animals together form a balance of life on the earth and that each 
is necessary for the other. Certain substances found in the 
body wastes of animals are necessary to the fife of a green plant. 



56 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

One of the most interesting relationships for study are those 
that exist between insects and flowers. Flowering plants, as we 
know, produce seeds and fruits, and from these come new genera- 
tions of plants. Not all of us realize, however, the very close 
dependence of these plants on the insects that visit them. If it 
were not for these insect visits, many plants would not produce 
seeds. 

In the latter part of the eighteenth century a German named 
Christian Konrad Sprengel worked out the facts that the structure 
of certain flowers seemed to be adapted to the visits of insects. 
Certain facilities were offered to an insect in the way of easy foot- 
hold, sweet odor, and food in the shape of pollen and nectar, the 
latter a sweet-tasting substance manufactured by certain parts of 
the flower known as the nectar glands. Sprengel further dis- 
covered the fact that pollen could be and was carried by insect 
visitors from the anthers or pollen-bearing organ of the flower to 
the top of the part that produced the seeds. It was not until the 
middle of the nineteenth century, however, that an Englishman, 
Charles Darwin, worked out further the relation of insects to 
flowers by his investigations on the cross-pollination of flowers. 
By this we mean the transfer of pollen from the pollen-producing 
organ of one flower to the seed-producing organ of another flower 
of the same kind. 

Many species of flowers are self-pollinated, but Charles Darwin 
found that some flowers which were self-pollinated did not produce 
as many seeds, and that the plants which grew from their seeds 
were smaller and weaker than plants from seeds produced by 
cross-pollinated flowers of the same kind. He also found that 
plants grown from cross-pollinated seeds tended to vary more 
than those grown from self-pollinated seeds. This has an important 
bearing, as we shall see later, in the production of new varieties 
of plants. Darwin studied for many years the pollination of 
flowers, and discovered in almost every case that showy, sweet- 
scented, or otherwise attractive flowers were most likely to be 
cross-pollinated by insects. He also found that, in the case of 
flowers that were inconspicuous in appearance, often a compensa- 
tion appeared in the odor which apparently rendered them attrac- 



INSECTS AND FLOWERING PLANTS 57 

live to certain insects. The so-called carrion flowers, pollinated 
by flies, are good examples, their odor being like that of decayed 
flesh. Other flowers, which open at night, are white and provided 
with a powerful scent so as to attract night-flying moths and other 
insects. All these and many other interesting facts about insects 
and flowers and their interrelationships will be found in the pages 
that follow. 

PROBLEM I. WHAT ARE SOME OF THE INTERRELATIONS 
BETWEEN PLANTS AND ANIMALS? 

Field Exercise. To determine whether conditions of mutual aid exist 
between insects and flowering plants. 

Materials. An insect net, cigar boxes containing sheets of cork, 
insect pins, and a cyanide bottle are useful. (Caution: Do not smell 
the cyanide ; the fumes are deadly poison.) 

Object of trip. The object of this trip is threefold : 

1. To find out some of the relations of mutual help existing between 
plants and animals. 

2. To learn to know a few common insects, and to collect them for 
later study. 

3. To have such an enjoyable time that you will wish to go again 
by yourself. 

Method. Your trip should include fields and waste lots covered with 
weeds and trees. Look for six-legged animals (insects) on plants. 
Do they receive any protection from such plants? Shelter? Food? 
Give examples under each of these headings. Do you find any insects 
laying their eggs upon plants ? Why do you think they do this ? 

Follow a bee until it alights on a flower. Try to find out exactly 
what it gets from the flower and how it does it. Xow observe where 
it goes next. Do bees visit flowers of the same kind in succession? 

Look for other flying insects that are on flowers. (Extra credit 
may be given for the working out of the relation between a butterfly 
and a flower.) 

Carefully observe the goldenrod blossoms for yellow and black 
beetles (locust borer) about an inch long. What are they doing? 
Observe grasshoppers or other insects on stalks of grass. What are 
they doing there? 

Strip the bark from fallen trees. Look carefully for any sigDs of 
living things. Collect any living animals you may see. If a small 
stream or pond is available, scrape or dredge through the aquatic 
plants near the shore and see what animals you can find. What are 
they doing there ? 

Dig into rich soil near the roots of grain or other plants and note what 
living animals may be there. Ask help from your instructor in their 
identification. 



58 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

Laboratory Exercise. How to identify an insect. If possible, use 
a living bee from an observation hive, although some observation may 
be made in the field and reported to the class. 

Examine its body carefully. Notice that it has three regions : a front 
part or head; a middle part, the thorax, divided into three portions or 
segments; and a hind portion, segmented 1 and hairy, the abdomen. 

How many pahs of legs does it have ? The legs, j ointed and provided 
with tiny hooks at the end, are attached to the thorax. Two pairs 
of delicate wings are attached to the upper or dorsal side of the thorax. 
To which segments of the thorax are they attached? The entire body 
has a tough covering or exoskeleton composed of chitin (kitin), a sub- 
stance chemically much like a cow's horn. This exoskeleton in the 
bee is partly covered with tiny hairs which form a vesture - over the 
body. The muscles, which provide for movement, are fastened to 
the interior of the exoskeleton, for there is no internal skeleton. 

Is there any movement of the abdomen of a living bee? The animal 
breathes through tiny openings called spiracles (spir'a-k'l), which are 
found on each segment of the abdomen and lead into branching air 
tubes. Bees have compound eyes composed of numerous units called 
ommitidia. Simple eyes or ocelli are usually also present. Bees are 
provided with a pair of jointed feelers called antennae. Wings are 
not found on all insects, nor is a vesture ; but the other structures just 
given are characteristics of the great group of animals we call insects. 



simple eye 

compouncC e^e. 

antenna 



heacC 



rtxcJe 




jsting 



The honeybee. How many of the parts labeled here can you find on your specimen ? 

Common forms of insects. Inasmuch as there are more than 
450,000 different kinds of insects, it is evident that it would be a 
hopeless task for us even to attempt to recognize all of them. 

1 Segmented (seg'ment-ed) : separated into sections or parts. 

2 Vesture (ves'tux) : a covering. 



COMMON FORMS OF INSECTS 59 

But we can learn to distinguish a few examples of the common 
forms that might be seen on a field trip. In the fields, on grass, or 
on flowering plants we may find members from at least six of 
the twenty orders of insects. These may be known by the follow- 
ing characters : 

The order Hymenoptera (hi-men-op'ter-d, membrane wings), 
to which the bees, wasps, and ants belong, is the only insect order 
of which some of the members are provided with true stings. 
This sting is placed in a sheath at the extreme hind end of the abdo- 
men. All structures which the honey bee has are possessed by 
this group of insects. 

Butterflies and moths will be found hovering over flowers. 
They belong to the order Lepidoptera (lep-i-dop'ter-d, scaled 
wings) (see p. 68). This name is given to them because their 
wings are covered with tiny scales, which fit into little sockets 
much as shingles are placed on a roof. The wings are always 
large and usually brightly colored; the legs are small, and 
one pair of them is often inconspicuous. These insects take 
liquid food through a long tubelike organ, called the proboscis 
(pr6-bos'is). 

Grasshoppers, found almost everywhere, katydids, and crickets, 
black grasshopper-like insects often found under stones, belong to 
the order Orthoptera (or-thop'ter-d, straight wings). Members of 
this group may usually be distinguished by their strong, jumping 
hind legs, by their chewing or biting mouth parts, and by the fact 
that the hind wings are folded up under the somewhat stiffer 
front wings. 

Another group of insects sometimes found on flowers in the fall 
are flies. They belong to the order Diptera (dip'ter-d, two wings) . 
These insects are usually rather small and have a single pair of gauzy 
wings. Some of man's worst enemies are found in this group of in- 
sects, which includes the house fly, mosquitoes, stable fly, and botfly. 

Bugs, members of the order Hemiptera (he-mip'ter-d, half 
wing), have mouth parts that are fitted for piercing and sucking. 
They are usually small and many of them have a pair of delicate 
membranous wings covered with outer wings which are somewhat 
thickened. 



60 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

The cicadas, aphids, 
and scale insects belong 
to the order Hoinoptera 
(ho-mop'ter-a, similar 
wings) . Their mouth- 
parts are formed for 
sucking. 

The beetles belong 
to the order Coleop- 
tera (kol-e-op'ter-d, 
sheath wings), and are 

A wasp stinging a caterpillar. Why is the wasp a member often Called " buSS " 
of Hymenoptera ? * 

by the uninformed. 
Any beetle will show the following characteristics : The body is 
usually heavy and broad. Its exoskeleton is hard and tough. 
This chitinous body covering is better developed in the beetles 
than in any other of the insects. The three pairs of legs are 





C. Clarice 
Two grasshoppers having an argument as to which one is to occupy that blade of grass. 



COMMON FORMS OF INSECTS 



61 



stout and rather short. 
The outer wings are 
hard and fit like a 
shield over the under 
wings, which are effi- 
cient organs of flight. 
The mouth parts, pro- 
vided with an upper 
and lower lip, are fitted 
for biting. They con- 
sist of heavy curved 
pincher-shaped mandi- 
bles (man-di-b'l), which 
are provided with palpi 




A water scorpion. Why is it classified as a member of 
Hemiptera ? 

(pal'pi), organs of taste and smell. 



Practical Exercise 1. Look up in a reference book the names of other orders 
of insects than those that have already been given. Give examples of insects 
in each of these orders. 




C. Clarke 
A June beetle lighting on a grape leaf and folding his wings under his brown wing covers. 



62 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

Self-Testing Exercise 

Everywhere in nature we find (1) (2) on plants or 

using them for (3) . Insects also are seen to visit (4) . 

(5) are the most numerous of all (6). An insect has 

(7) body parts ; (8) pairs of legs ; an exoskeleton 

composed of (9) and breathes through (10). The 

eyes are (11). The parts of the insect's body are called the 

(12), (13), and (14). Bugs have mouth 

parts fitted for (15) and (16). Beetles have 

(17) pairs of wings, the outer acting as a (18) for the delicate 

inner pair. Grasshoppers (19) their food. Some of man's 

worst enemies are members of the order (20) . Bees and wasps 

are able to (21). 



PROBLEM II. TO KNOW SOMETHING OF THE STRUCTURE 
AND LIFE HISTORY OF THE GRASSHOPPER 

Laboratory Exercise. Use living red-legged grasshoppers if possible. 
Find the three parts : head, thorax, and abdomen. Is there an exo- 
skeleton ? 

Find the three segments in the thorax? They are called from 
anterior to posterior, prothorax, mesothorax, and metathorax. Which 
bear legs? Which bear wings? The membrane-like wings, out- 
growths of the body, lie straight along the back when at rest. 

Study the hind leg carefully. Compare it with the diagram. Can 
you find all these parts? Move the leg. How is it used? Can 



Mead.. t , _thort»c 



abdomen. 



cmlzrma — 
simple eye 
Compound «^e 




jggtf lay. 



er* 



Identify these parts in your specimen. 

you find any adaptations? How are the wings placed when not in 
use? When flying? Are there any differences in the two pairs of 
wings ? - Into how many segments is the abdomen divided ? Are all 



MUSCULAR ACTIVITY 



63 



of them complete? The end of the abdomen is modified in the female 
into an ovipositor or egg layer (see diagram). 

On each side of the abdomen in eight of the segments (in the red- 
legged grasshopper) are found tiny openings called spiracles. There 
are also two pairs of spiracles on the thorax. These spiracles open into 
little tubes called tracheae (tra/ke-e). The tracheae divide and subdi- 
vide like the branches of a tree, so that all parts of the body cavity are 
reached by their fine endings. Is there any movement of the abdomen 
of the living grasshopper? Describe this movement. Air is drawn in 
by the expansion of the abdomen and forced out when it contracts. 
By means of the tracheae, air is brought in contact with the blood. 

Muscular activity. Insects have the most powerful muscles of 
any animals of their size. Relatively, an enormous amount of 
energy is released during jumping or flying. The tracheae pass 
directly into the muscles and other tissues so that a supply of 
oxygen is directly at the place where energy is being released. 



.Simple Compound 




6in$e unit of 
compound 
eye of worker 
laonejrloee^ 



lov^er lip 
Find the knife and fork of the grasshopper. 



liboffemeftt 
r"TneTn.torwie, 
L. nerve fiber 

What two insect heads are shown here ? 
Read your text carefully. 



Food taking. The grasshopper is provided with two pairs of 
jaws, a fork-like pair, the maxillae (mak-sil'e), and a pair of hard 
toothed jaws, the mandibles. These parts when not in use are 



64 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



covered by two flaps, the upper and lower lips. The leaf upon 
which the grasshopper feeds is held in place in the mouth by means 
of the maxillae, while it is cut into small pieces by the mandibles. 
Eyes. An examination of the compound eye of a grasshopper 
with a lens shows the whole surface to be composed of tiny six- 
sided lenses called facets (fas'ets). Each facet marks the surface 

of a unit (ommati- 



dium) of the com- 
pound eye. Each 
unit probably gives a 
separate impression 
of light and color. 
Since each unit is 
separated from its 
neighbor by a layer 
of pigment, a com- 
pound eye is most 
favorable for per- 
ceiving the move- 
ment of ob j ec ts . The 
grasshopper also has 
three simple eyes, or 
ocelli, on the front of 

the head. The simple eyes probably are able only to perceive 

light and darkness. 

Practical Exercise 2. Explain why an insect easily perceives a moving object. 

Other sense organs. The segmented feelers, or antennae, have 
to do with the sense of touch and smell. The auditory organ or 
ear of the grasshopper is found under the wing on the first segment 
of the abdomen. Covering the body and on the appendages are 
found sensory hairs which make the insect sensitive to touch. 
Thus the armor-covered animal is put in touch with its 
surroundings. 

Life history. In the fall of the year the female grasshopper 
digs a hole in the ground. She thrusts her abdomen into the hole 
and lays from twenty to thirty eggs in small oval or bean shaped 




Life history of a grasshopper. Explain what is meant by a 
life cycle ; a metamorphosis. 



GRASSHOPPERS 65 

puc&ets. These hatch out in the spring as tiny wingless grass- 
hoppers called nymphs. The young insects molt or cast off their 
hard exoskeleton several times. At each shedding of the " skin " 
the grasshopper gets larger. Since this molting results in a series 
of changes in form from the young nymph to an adult with wings, 
the whole process is called a metamorphosis or change of form. 
The grasshopper is said to have an incomplete metamorphosis 
because the changes in form are not great. The nymphs can be 
recognized in the earliest stages as grasshoppers. 

In the fall most of the adults die, only a few surviving the winter. 
In the South and West, some grasshoppers have more than one 
brood in a summer, which makes them more numerous and there- 
fore more of a pest to the farmers. 

Relatives of the grasshoppers. Among the near relatives of 
the grasshopper are the brown and black crickets, cockroaches, 
" waterbugs," katydids, praying mantis, and many others. 

Self-Testing Exercise 

Grasshoppers belong to the order (1) because they have 

wings placed (2) along the back. The mouth parts are fitted 

for (3). The organs of touch in insects are called (4), 

the organ of hearing, the (5), is usually found under the 

(6) . Insects which pass through a series of (7) 

before they (8) adults are said to undergo a (9). 

Insects have to (10) in order to grow larger. 

PROBLEM HI. HOW TO KNOW SOMETHING ABOUT THE 
STRUCTURE AND LIFE HISTORY OF A BUTTERFLY 

. Laboratory Exercise. Examine a butterfly carefully with a mag- 
nifying glass. What do you find covering the body and wings? Note 
that the legs are smaller and weaker than those of the grasshopper. 
How many pairs do they have? Are they all the same size? Ex- 
amine a small portion of a wing under a compound microscope. Draw 
a scale showing how it fits into the membranous wing. What name 
is given to this order of insects? Why? The mouth parts of the 
butterfly are modified into a long proboscis, a sucking tube through 
which the insect sucks nectar from the flowers. 

Practical Exercise 3. Prepare the life histories of several different butter- 
flies. If possible, use material that you have collected and mounted. 



66 HOW ARE ANIMALS AND PLANTS DEPENDENT? 




C. Clarke 



The life history of the 
monarch butterfly. If it is 
possible to find some milk- 
weed on our trip, we are 
quite likely to find hovering 
near it a golden brown and 
black butterfly, the monarch 
or milkweed butterfly. The 
female frequents the milk- 
weed in order to lay eggs; 
she may be found doing this 
at almost any time from 
June until September. 

Egg and larva. The eggs, 
tiny mound-shaped dots, a 
twentieth of an inch in 
length, are fastened singly 
to the under side of milk- 
weed leaves. Some instinct 
leads this butterfly to de- 
posit her eggs on the milk- 
weed, for the young feed 
upon this plant. The eggs 
hatch out in four or five 
days into caterpillars. Each 
caterpillar will shed its skin 
several times before it is full 
grown. These caterpillars 
possess, in addition to the 
three pairs of true legs, four 
pairs of prolegs which are 
fleshy structures found on 



The female monarch butterfly lays 
her eggs on the edge of the milkweed 
leaf. The egg hatches and the green, 
black, and white caterpillar feeds on 
the milkweed. Later the caterpillar 
fastens itself to the midrib of a leaf. 



BUTTERFLIES 



67 



the abdominal segments. 
The animal at this stage is 
known as a larva. 

Formation of pupa. After 
a life of a few weeks at most, 
the caterpillar stops eating 
and begins to spin a tiny mat 
of silk upon a leaf or stem. 
It attaches itself to this web, 
head downward, and sheds 
its skin again. After this 
molt, it is without legs or 
mouth parts. It hangs to the 
stem in a dormant stage and 
is known as the chrysalis 
(kris-d-lis) or pupa. During 
this stage many changes take 
place and the caterpillar 
gradually changes into a 
butterfly. 

The adult. After some 
weeks of inactivity in the 
pupa state, the pupa case 
splits along the back, and 
the adult butterfly emerges. 
At first the wings are soft and 
much smaller than in the 
adult. Within fifteen min- 
utes to half an hour after the 
butterfly emerges, however, 
the wings expand and dry, 
and the insect is ready to fly 



The skin splits and a light green chrys- 
alis emerges, which gradually changes 
its shape. After a time the butterfly 
comes out of its chrysalid shell. It clings 
to the shell, spreading and stretching his 
wings until they are dried and strength- 
ened. 




68 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

'4 k antenna 





..sucking tube 
How do the structures you found in your specimen compare with these in the diagram? 

away. The female insect, after her marriage flight, deposits her 
eggs on a milkweed plant. 

Since this butterfly in most parts of the United States has at 
least two broods a year and since the young feed on the milkweed 
and dogbane, both common weeds, we see some cause for its 
wide distribution and great numbers. The metamorphosis of the 
butterfly is said to be complete because it 
passes through several distinct changes of 
form. 

Moths. Moths are familiar to most of us, 
but they can usually be seen only at night be- 
cause of their night-flying habits. Certain 
differences between them and butterflies are 
noted in the following table : 



Butterfly 
Antennae threadlike, usually knobbed at tip. 
Fly in daytime. 

Wings held vertically when at rest. 
Pupa naked. 

Moth 
Antennae feathery or threadlike, never 
knobbed. 

Usually fly at night. 




..simple 
eye 

true leg 
Spiracle 



- proleg 



anal ^ 
proleg 

anal horn. 



Caterpillar of moth. Find 
the parts of the adult insect 
here. Does this agree with 
your definition of an insect ? 



WASPS 



69 



Wings held horizontally or folded over the body when at rest. 
Pupa usually covered by a cocoon or case. 

The Promethea moth, the Polyphemus or American silkworm 
moth, and the Cecropia moth are among the largest and most 
commonly collected. 

Self-Testing Exercise 

Butterflies are called (1) because of the (2) on the 

wings. The adults lay their (3) on plants which the 

(4) will feed upon. This stage is followed by the (5) stage. 

In this stage the chrysalis is usually attached by a (6) 

(7) to the (8) plant. 



X 



PROBLEM IV. WHAT DO WE MEAN BY COMMUNAL LIFE 
AND DIVISION OF LABOR? 

Individual Projects. Give a report on the life habits of a solitary wasp. 
Work out with diagrams the life history of some communal insect. 
Keep a hive of bees and report to the class on their habits. 
Make an ants' nest and keep a colony of ants in it. 

Solitary wasps. Some bees and wasps lead a solitary existence, 
the digger wasps being an example. Each female wasp burrows 
in the ground or in 
wood and constructs 
a nest in which she 
lays her eggs. The 
nest is provisioned 
with spiders and in- 
sects which are not 
killed but are stung 
into insensibility. 
The nest is closed up 
after food is sup- 
plied. When the 
young hatches it 
finds plenty of food 
near at hand to 
nourish it during its 
growth. 

h. bio — 6 




stoned 
fill 



1TOO 

•paralyse** inch.--v.b-r™. 
v into burrow -.t 



Explain this life history of a solitary wasD. 




70 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



Bumblebees. In the life history of the bumblebee we see the 
beginning of the instinct to live together. Some of the female 
bees (known as queens) burrow into the ground in the fall and sleep 
all winter. They lay their eggs the following spring in masses of 

pollen, which they 
^ : gather and place in 

holes in the ground, 
often in a deserted 
mouse hole. The 
young hatch as larvae, 
then pupate, and 
finally become workers 
(imperfect females) in 
which the egg-laying 
apparatus, or ovi- 
positor, is modified to 
be used as a sting. 
The workers bring in 
pollen to the queen, 
in which she lays her 
eggs. Several broods 
of workers are raised 
during a summer. In 
the early fall a brood of males and egg-laying females or queens 
are produced instead of workers. The males leave the hive as 
soon as they are able to fly, and never return. They mate with 
the queens and then die. They live in all about three or four 
weeks. The young queens also leave the hive, although they 
occasionally return. By means of these queens the brood is 
started the following year. 

Practical Exercise 4. Report on the life story of some South American 
wasps. Read Howe's Insect Behavior, Chapters ii and iv-xii inclusive. 

The Honeybee. The most wonderful communal life has been 
developed among the honeybees. 1 

1 Their daily life may be easily watched in the schoolroom, by means of one of the 
many good and cheap observation hives now made to be placed in a window frame. 
Directions for making a small observation hive for school work can be found in 




«#" 



Compare the life history of the bumblebee with that of the 
solitary wasp. How does it differ ? 



THE HONEYBEE 



71 



The colony in a hive usually consists of a queen, a few hundred 
drones, or males, and several thousand imperfect females known 
as workers. A prosperous colony may have 50,000 to 75,000 
members. The division of labor is seen best in a hive in which 
the bees have been living for some weeks. The queen, a virtual 
prisoner, does nothing except lay eggs, sometimes as many as 
fifteen hundred a day, and keeps this up, during the warm weather, 
for from two to five years. Most of the eggs are fertilized by the 
sperm cells of a male and develop into workers ; the unfertilized 
eggs develop into males or drones. After a short existence in the 
hive the drones are usually driven out by the workers. 

The cells of the comb are built by the workers out of wax 
secreted from the under surface of their bodies. The wax is 
cut off in thin plates by means of the wax shears between the 
two last joints of the hind legs. The cells of the comb are made 
in two layers, back to back, opening on opposite sides. They are 
hexagonal in cross sec- 
tion and are of differ- 
ent sizes, the smaller 
cells being used for 
honey storage and for 
the development of 
the workers, the larger 
cells for housing the 
drones. The queen 
lays one egg in each 
cell, and the young are 
hatched after three 
days, to begin life as 
white footless grubs. 
For a few days they 
are fed on partly di- 
gested food called bee jelly, regurgitated * from the stomach of 
the. youngest workers or nurses. Later they receive pollen and 

Hodge, Nature Study and Life, Chapter xiv. Bulletin No. 1, U. S. Department of 
Agriculture, entitled The Honey Bee, by Frank Benton, and Farmers' Bulletin 447 
on Bees, by E. F. Phillips, give useful information to the bee keeper. 
1 Regurgitate (re-gur'ji-tat) : to cast out again from the stomach. 




Xuture Magazine 

Young queen bees sometimes rebel against the old 

queen, and leave the hive, followed by a large portion of 

the colony. In this picture, some of the " striking " bees 

are shown returning to their original home. 



72 HOW ARE ANIMALS AND PLANTS DEPENDENT? 





w 


*i;lfe. s . 






^S^M 








>wA;M-^ 










f,.''^K^'S:'''S : ^ 


~ »i 






%:KM^ 


. 


/' '*% 






'=* 


i 1 






1 ik** 


^w 








/ ¥ 









honey to eat. A little of this 
mixture, known as bee bread, 
is put into the cells, and the 
lids covered with wax by the 
working bees, and the young 
larvae allowed to pupate. 
After about two weeks of 
quiescence in the pupal state, 
it changes into a fully de- 
veloped adult and chews its 
way out of the cell. It takes 
its place in the hive, first 
caring for the young as a 
nurse, later making excur- 
sions to the open air after 
food as an adult worker. 

If a new queen is to be 
produced, several of the cell 
walls are broken down by 
the workers, making a large 
ovoid l cell in which one egg 
is left. The young bee in this cell is fed during its whole larval life 
upon royal jelly, and grows into a bee of much larger size than an 
ordinary worker. When a young queen appears, great excitement 
pervades the community ; the bees appear to take sides ; some re- 
main with the young queen in the hive, while others follow the old 
queen out into the world. This is called swarming. They usually 
settle around the queen, often hanging to the limb of a tree. While 
the bees are swarming, certain of the workers, acting as scouts, de- 
termine on a site for their new home; and, if undisturbed, the 
bees soon go there and construct their new hive. This instinct is 
of vital importance to the bees, as it provides them with a means 
of forming a new colony. A swarm of domesticated bees may be 
easily hived in new quarters. 

Division of labor in the hive. The work of the hive is divided 
among the various kinds of bees in a most interesting manner. 

1 Ovoid (6 'void) : egg-shaped. 



C. Clarke 
A honeybee, in search for nectar, has become cov- 
ered with grains of hollyhock pollen. 



THE HONEYBEE 



73 



We have seen that the queen lays all the eggs, acting as a sort of 
tribal mother. The eggs are all fertilized by one drone, who 
places the sperm cells within the body of the queen on her nuptial 
flight. The young workers feed the larvae and act as nurses. 
The older bees take turns in a number of duties ; some attend to 
the queen and drones, some act as sanitary police, keeping the 
hive clean of dirt and bodies of dead bees, others ventilate the 
hive by buzzing with their wings, while many others work in the field 
gathering pollen and nectar from flowers. 

The nectar is swallowed and kept in the crop, or honey stomach, 
until after the bee returns to the hive, where it is regurgitated 
into the cells of the comb. It is now thinner than what we call 
honey. To thicken it, the bees swarm over the open cells, moving 
their wings very rapidly, thus evaporating some of the water in 
the honey. A hive of bees has been known to make over thirty- 
one pounds of honey in a single day, although the average is very 
much less than this. 




C. Clarke 
A tiny ant drags home a cabbage butterfly, to add to its store of food, which is needed for the 

young. 



74 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

Ants. Ants are the most truly communal of all the insects. 
Their life history and habits are not so well known as those of the 
bee, but what is known shows even more wonderful specialization. 

The nest of a colony consists of underground galleries with 
enlarged storerooms, nurseries, etc. The inhabitants of a nest 
may consist of winged males and females, and wingless workers, 
which act as gatherers of food, nurses, and protectors. We may find 
ant nests almost anywhere in our yards or gardens. Many nests 
are found under large flat stones, chiefly because stones hold the 
heat of the sun and keep the nest from cooling too rapidly at night. 

The entire communal life of the ants might be said to be 
based upon the perception of odor. If an ant, although one of the 
same species, is put into a colony to which it does not belong, it 
will be set upon and either driven out or killed. Ants never 
really lose their community odor ; those absent for a long time, on 
returning, apparently will be easily distinguished by their odor, and 
eagerly welcomed by the other members of the nest. The commu- 
nication of ants, as seen when they stop each other, away from the 
nest, is evidently a process of smelling, for they caress each other 
with the antennae, the organs with which odors are perceived. 















■' - ' £ | 





Paul G. Howes 
Some ants live on a sweet fluid which is given off by aphids or plant lice. They induce the 
aphids to exude this fluid by stroking them with their antennae. Such aphids are carefully 
watched and cared for by the ants. 

Ant larvae are called grubs. They are absolutely helpless and 
are taken care of by nurses. The pupae may often be seen as 
they are being carried in the mouths of the nurse ants, who bring 
them to the surface for sun and air. They are wrongly called 
ants' eggs in this stage. 



CHARACTERISTICS OF INSECTS 75 

Some species of ants are among the most warlike of any insects. In 
the case of the robber ants, which live entirely by war and pillage, the 
workers have become modified in structure, and can no longer work, 
but only fight. Some species go further and make slaves of the ants 
preyed upon. These slaves do all the work for their captors, even 
to making additions to the nest and acting as nurses to their young. 

Practical Exercise 5. Report on the life in an ant colony in South America as 
described in Beebe's Jungle Days, or the life of the army ants, Chapter xiv, in 
Howe's Insect Behavior. 

Self-Testing Exercise 

Some wasps lead (1) lives but most (2), (3), 

and wasps show (4) life. In the case of the honeybees we 

have a (5) with a single fully-developed (6) or 

(7), several hundred (8) or (9) and man? 

thousands of (10). The latter have many duties such as 

gathering (11) and (12) from flowers, (13) 

the young, (14) and (15) the hive. They also make 

(16), which they store in cells made of (17). Ants 

also have a complicated communal life, some acting as (18), 

others as (19), and still others as (20). The com- 
munal life of ants is dependent upon (21). Each colony seems 

to have its own peculiar (22). Bees, ants, and wasps belong to 

the order (23). 

PROBLEM V. WHAT ARE THE CHARACTERISTICS OF OTHER 
GROUPS OF INSECTS? 

The Flies. There is an order of insects called Diptera, which 
is characterized by having only two gauzy wings. The members of 
this group of insects frequently found on a field trip are mosquitoes, 
gnats, botflies, and the house fly. 

The head of the common fly is freely movable and is provided 
with mouth parts for sucking and lapping. The foot shows wonder- 
ful adaptation for clinging to smooth surfaces, as it is provided with 
sticky pads bearing tubelike hairs. 

The second pair of wings is changed into a pair of small knobs, 
called balancers. This name suggests their use, for if they are re- 
moved, the fly is unable to balance itself. 

The development of the fly is extremely rapid. A female may 



76 HOW ARE ANIMALS AND PLANTS DEPENDENT? 




Why does the house fly belong to the order of insects known 
as Diptera? 



lay from one hun- 
dred to two hundred 
eggs. These are 
usually deposited in 
garbage or manure. 
In warm weather, 
within a day after 
the eggs are laid, 
the young maggots, 
as the larvae are 
called, hatch. After 
about one week of 
active feeding, these 
wormlike maggots 
become quiet and 
go into the pupal stage, whence under favorable conditions they 
emerge within less than another week as adult flies. The adults 
breed at once, and in a short summer there may be over ten 
generations of flies. This accounts for the great number of flies 
in late summer. Fortunately few flies survive the winter. 

Practical Exercise 6. Discuss the fly problem as it exists in your commu- 
nity. What steps might you take to abate the fly nuisance ? 

The life history of a beetle. The May beetle or June bug and 

potato beetle are examples of beetles. Many beetles lay their 

eggs in the ground, 

where they hatch 

into cream-colored 

grubs. A grub differs 

from the maggot or 

larva of the fly in 

possessing three pairs 

of legs. These grubs 

live in burrows in the 

ground, where they 

feed on the roots of 

grass and garden 

plants. The larval 




5 to 14 Act 

mcmtcrie necxp 

'to 



Compare the life history of the fly with that of the bumblebee. 




THE CICADA 



77 



form remains underground from two to three years, the latter 
part of this time as an inactive pupa. During the latter stage 
it lies dormant in an ovoid area excavated by it. Eventually 
the wings (which are budlike in the pupa) grow larger, and the 
adult beetle emerges fitted 
for its life in the open air. 

This group of insects in- 
clude some of man's best 
friends, as the ladybird 
beetle, and some of his 
worst enemies, as the po- 
tato beetle. 

Life history of the ci- 
cada. The seventeen-year 
cicada lays her eggs in slits 
which she makes in the 
twigs of trees. Immedi- 
ately after hatching, the 
young drop to the ground 
and bury themselves in the * 

, rp, . , , » The full grown larva of the Colorado potato beetle 

earth. lney Stay there IOr drops to the ground and burrows in the soil, forming 

seventeen years. In the a pupa. 

South these insects live only thirteen years underground. They 
obtain their food by sucking the juices from the roots of plants. 
During this stage they somewhat resemble the grub of the beetle 
(June bug) in habits and appearance. When they are about to 
molt into an adult, they climb above the ground, and fasten 
themselves to some firm object, as a wooden fence or a tree 
trunk. The skin then splits along the back and the adult cicada 
emerges. 

Aphids. The aphids are among the most interesting of the 
Homoptera. They are familiar to all as tiny green lice seen swarm- 
ing on the stems and leaves of the rose and other cultivated plants. 
They suck the juices from stem and leaf. Plant lice have a 
remarkable life history. Early in the year the eggs develop into 
wingless females which produce living young, all females. These 
in turn reproduce in a similar manner, until the plant on which 




78 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

they live becomes overcrowded and the food supply runs short. 
Then a generation of winged aphids is produced. These fly away 




y jgrovnd. on 
~ Sap from roots 



Life history of the seventeen-year cicada. What are the chief differences 
between this life history and the others shown ? 



to other plants, and reproduction goes on as before until the 
approach of cold weather, when males and females appear. Ferti- 
lized eggs are then produced which give rise to young the following 
season. 

Dragon flies and their relatives. The dragon fly receives its 
name from the fact that it preys on insects. The adult eats 
mosquitoes and other insects which it captures while flying. Its 
four large, lacelike wings give it power of very rapid flight, while 
its long, narrow body is admirably adapted for the same purpose. 
The large compound eyes placed at the sides of the head give 
keen sight. It possesses powerful jaws (almost covered by the 
upper and lower lips). 

These insects deposit their eggs in the water, and the fact that 
they may be often seen with the end of the abdomen curved down 



DRAGON FLIES 



79 



under the surface of the water in the act of depositing the eggs 
has given rise to the belief that they were then engaged in sting- 
ing something. The egg hatches into a form called a nymph, 
which in the dragon fly is characterized by a greatly developed 
lower lip. When the animal is at rest, the lower lip covers the 
large biting jaws, which can be extended to grasp and hold its 
prey. It may live as a nymph from one summer to as long as 
two years in the water. It then crawls out on a stick, molts 
by splitting the skin down the back, and comes out as an 
adult. 

A closely related form is the damsel fly. This may be distin- 
guished from the dragon fly by the fact that when at rest the wings 
are carried close to the abdomen, while in the dragon fly they are 
held in a horizontal position. 

Another near relative of the dragon fly is the May fly. These 
insects in the adult stage have lost the power to take food. Most 
of their life is passed in the larval stage in the water. The adults 
sometimes live only a few hours, just long enough to mate and 
deposit their eggs. These insects belong to the order Odonata. 




> •* 




A dragon fly that has just emerged from the nymph. 



80 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

Self-Testing Exercise 

The hind wings of the flies are for (1). The (2) 

of a fly is a maggot. The beetle has a larval stage called a (3), 

which has (4) pairs of (5). A dragon fly in the larval 

stage is called a (6). Aphids (7) their food and do 

much harm in the (8) 



PROBLEM VI. WHY ARE INSECTS SO NUMEROUS? 

There are over 450,000 different known species of insects, or 
almost three times as many as all other animals put together. 
From the standpoint of numbers they are a successful group. 
Why is this so? Several reasons can be given. Scores, often 
hundreds, of eggs are laid by a single mother, and sometimes before 
a month has passed each little female insect that has hatched is 
ready to lay eggs in its turn. This life cycle may be repeated sev- 
eral times during a season. They grow rapidly, they are often 
adapted to use food that other animals will not use, as witness the 





C. Clarke C. Clarke 

The moth clinging to the trunk of an elm tree The yellow crab spider on the yellow center of 

is so similar in coloring to the bark that it is the flower and the white crab spider against the 

not noticeable at a distance. background of white petals are inconspicuous 

as they lie in wait for some visiting insects. 



HOW ARE INSECTS PROTECTED? 



81 




hundreds of forms that 
live on weeds and decayed 
food, and they have nu- 
merous ways of escaping 
their enemies. Such is the 
house fly. On the other 
hand, such insects have 
many enemies so that few 
forms become over abun- 
dant. Many can fly and 
thus have an easy way of 
escaping their enemies. 
Then many species are 
very tiny, thus escaping 
detection. The fact that 
many species pass through 
a metamorphosis is an un- 
doubted advantage, for 
often there is a long qui- 
escent stage either passed 
out of sight in the ground 
or under bark of trees or 
stones. The pupae of 
many insects are covered, 
so that birds or their ene- 
mies would not notice them. Many adults have either a hard body 
covering or are covered with hairs. In addition many have odor 
or taste disagreeable to birds, which are their chief enemies. 

If we examine insects in their native haunts, we find that many 
of them have interesting means of protection. The grasshopper 
is colored like the grass on which it lives. The katydid, with 
its green body and wings, can scarcely be distinguished from the 
leaves on which it rests. The walking stick, which resembles the 
twigs on which it is found, and the walking-leaf insect of the tropics 
are other examples. This is called protective resemblance. 

Some insects are provided with means of defense, such as poison 
hairs or stings. Those animals which are harmful are sometimes 



■^ _^ 


if 



C. Clarke 
The viceroy butterfly (above) mimics the monarch 
butterfly, which is distasteful to birds, and thus gains 
protection from its enemies. 



82 HOW ARE ANIMALS AND PLANTS DEPENDENT? 






Paul Greswold Howes 
A leaf hopper mimics the central part of the flowers upon which it was found. 
Find the insect. 

brightly colored or marked as if to warn animals to keep off or to 
take the consequences. They are said to show warning coloration. 
Examples of such insects may be seen in many varieties of beetles, 
especially the spotted ladybirds and potato beetles. Wasps show 
yellow bands, while many forms of caterpillars are conspicuously 
marked or colored. 

Larvae of insects, such as caterpillars, which are harmless, are 
brightly colored and protrude horns, or pretend to sting when 
threatened with attack. These animals appear to mimic animals 
similar in appearance, which really are protected by a sting or by 
poison. Some butterflies which birds eat look like those that are 
avoided by them and, therefore, must be distasteful. Such imita- 
tion is particularly well shown by the monarch and the viceroy 
butterflies. Some harmless flies imitate bees, and thus seem to 
receive a certain protection. When a harmless insect resembles 
a harmful one, we call it mimicry. 

Practical Exercise 7. Write a paragraph giving reasons why insects are 
more numerous than other forms of animals. 

Field Exercise. Find, mount, and exhibit to the class different 
examples of insects showing protective resemblance, warning color- 
ation, and mimicry. 



A SIMPLE FLOWER 83 

Self-Testing Exercise 

Protective coloring or resemblance is seen in the (1) 

(2) and (3). Protective mimicry is seen in the 

(4) and (5) butterflies. Insects are a (6) 

group. Many insects (7), and thus escape their enemies. 

The (8) stage is a help, because it provides a long quiescent 

(9) during which the insects are hidden from sight, Many 

insects are (10) colored. 

PROBLEM VH. OF WHAT USE ARE FLOWERS TO PLANTS? 

Laboratory Exercise. The structure of a simple flower. 

The floral envelope. Examine a simple flower, such as a lily. The 
expanded portion of the flower stalk, which holds the parts of the 
flower, is called the receptacle. The green leaflike parts covering the 
unopened flower, when taken together, are called the calyx. Each of 
these parts is a sepal. How many petals does your specimen have? 
What use do they seem to have ? The more brightly colored structures 
are the petals. How many do you find? When joined together, the 
petals form a corolla. The corolla is of importance in making the flower 
conspicuous. Of what value would this be? Frequently the petals or 
corolla have bright marks or dots which lead down to the base of the 
cup of the flower, where a sweet fluid called nectar is secreted by nectar 
glands. It is principally this food substance, later made into honey 
by bees, that makes flowers attractive to insects. 

The essential organs of the flower consist of the stamens and 
pistil (or pistils), the latter being in the center of the flower. How 
many stamens do you find in your specimen? Cut crosswise through 
the swollen part of the pistil. How many divisions do you find? 
Are the parts of the flower in multiples of each other? In a single 
stamen the boxlike part at the end is the anther; the stalk which 
holds the anther is called the filament. The anther is in reality a 
hollow box which produces a large number of little grains called 
pollen. Each pistil is composed of a rather stout base called the 
ovary, which contains the ovule or future seeds, and a more or less 
lengthened portion rising from the ovary called the style. The upper 
end of the style is called the stigma. 

Practical Exercise 8. Draw a longitudinal section of the flower and label 
all parts. Show the essential organs in color. 

Pollen. Pollen grains of various flowers, as seen under the micro- 
scope, differ greatly in form and appearance. Some are relatively 
large, some small, some rough, others smooth, some spherical, and 
others angular. They all are alike, however, in having a thick wall, 
with a thin membrane under it, the whole inclosing a mass of pro- 



84 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



stamen 



toplasm. At an early stage the pollen grain is a single cell, but at 
the time of pollination it contains two or three cells. 

Germination of pollen grains. Pollen grains will germinate 
if they fall on the stigma of a flower of the same kind of plant. 
The stigma secretes a sticky fluid containing sugar and certain 
acids, which the pollen absorbs and grows by sending out a thread- 
like tube which causes 
srtigmcc— ■ - ^ the growt h f the 

structure. During 
this growth, two nuclei 
are found in the tube. 
One of them, the tube 
nucleus, disappears 
after a time. The 
second, or germinative 
nucleus, divides to form 
two sperm nuclei. 

Fertilization. If we 
cut the pistil of a large 
flower (as a lily) length- 
wise, we notice that 
the style appears to be 
composed of rather 
spongy material in the 
interior; the ovary is 
hollow and is seen to 
contain a number of 
rounded structures 
which appear to grow 
out from the wall of 
the ovary. These are 
the ovules. The ovules, 
under certain condi- 
tions, become seeds. 
The central part of the 
style is found to be either hollow or composed of a soft tissue 
through which the pollen tube can easily grow. In germinating, 




-Mxeceptcrcle 



Parts of a complete flower. A flower is called perfect if it 
contains the essential organs. 



FERTILIZATION 



85 



the pollen grain sends out a pollen tube which grows downward 
through the spongy center of the style, following the path of least re- 
sistance, to the space within the ovary, and there enters an ovule 
through a tiny opening in the ovary wall, the micropyle (ml'cro-pllj. 

jS-JTi pollen 

"^£: anther 

pollen. 

tube. 



rcpyte 




ovule 
nucleus 



Read carefully the paragraph on fertilization and then explain 
this diagram in your workbook. 

During the growth of the pollen tube the sperm nucleus passes down 
the elongating tube. When the tube reaches a clear area of proto- 
plasm, known as the embryo sac, its tip is ruptured and the sperm nu- 
cleus passes out into this sac. The embryo sac is an ovoid space, 
microscopic in size, filled with semifluid protoplasm containing sev- 
eral nuclei. One of the nuclei, with the protoplasm immediately 
surrounding it, is called the egg cell. It is toward this cell that the 
sperm nucleus of the pollen tube grows. Ultimately the sperm nu- 
cleus reaches the egg cell and unites with it. The union of the 
sperm nucleus with the nucleus of the egg cell in the ovule is known 
as fertilization. The union of the sperm nucleus and the egg cell re- 
sults in sl fertilized egg. This egg, by constant divisions of the cells, 

H. BIO 7 



86 HOW ARE ANIMALS AND PLANTS DEPENDENT? 




#?' 











Pollen grains may take 
various forms. What might 
be the value of the spine- 
Explain, with reference to your text, the stages in the like structures on the pollen 
germination of a pollen grain. grains ? 

forms an embryo or baby plant. This is contained in the seed 

and, as we know, will develop into an adult plant if given proper 

environmental conditions. 

Practical Exercise 9. Make a series of diagrams to show just how the 
sperm nucleus reaches the egg cell in order to bring about fertilization. 
Make an enlarged diagram to show how fertilization takes place. 

Self-Testing Exercise 

The parts of a flower are (1), (2), (3), 

(4), and (5). Essential organs are the (6) 

and the (7). Pollen is produced in the (8). Egg 

cells are found in the (9). Fertilization of the (10) 

by a (11) nucleus from the pollen (12) causes 

an (13) or (14) plant to be formed. 

PROBLEM VIII. HOW ARE FRUITS FORMED? 

Laboratory Exercise. Examine an unopened pea or bean pod. 
Compare it with a pea or bean flower or with drawing. Find the 
parts of the flower in the fruit. What becomes of the petals and se- 
pals? What happens to the pistil? Where do the seeds grow? 

The pod of a bean, pea, or locust illustrates well the growth 
from the flower. The flower stalk, the ovary, and the remains 
of the style, the stigma, and the calyx, can be found on most 



FORMATION OP FRUITS 



87 




Can you find all parts of the flower in the ripened fruit ? 

unopened pods. If the pod is opened, the seeds will be found 
fastened to the ovary wall each by a little stalk called the funiculus 
(f u-nik'u-rws). That part of the ovary wall which bears the seeds is 
the placenta (pld-sen'td). The walls of the pod are called valves. 

The pod, which is in reality a ripened ovary with other parts 
of the flower attached to it, is considered a fruit. By definition, 
a fruit is a ripened ovary together with any parts of the flower that 



^^^^^ 


t^t^ ^pp 






^Sgp 


**" :<, V5 




* W 


'%: 




* ; 'V 


» . 


^ s : 1 









U. S. Department of Agriculture 

Why have so few grains appeared in this ear of corn ? Remember the corn cob bears 
pistillate flowers ; the " silks " are the long styles with stigmas at the tips. 



88 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

may be attached to it. The chief use of the fruit is to hold and to 
protect the seeds ; it may ultimately distribute them where they 
can reproduce young plants. 

Each seed has been formed as a direct result of the fertilization 
of the egg cell (contained in the embryo sac of the ovule) by a 
sperm nucleus of the pollen tube. 

Practical Exercise 10. Describe with the aid of diagrams the growth into 
a fruit of some flower, not given in the text. 

Self-Testing Exercise 

In a pod, the seed is fastened to the ovary wall by the (1). 

The (2) is the part of the wall of pod that bears the 

(3). The pod is a (4) (5) and is called a 

(6). The chief use of the (7) is to protect the 

(8) . Seeds are formed as a direct result of the (9) 

of the (10) cell in the embryo sac by the (11) nu- 
cleus in the (12) tube. 

PROBLEM IX. WHAT ARE SOME ADAPTATIONS IN INSECTS 
FOR CARRYING POLLEN? 

Insects as pollinating agents. Insects often visit flowers to 
obtain pollen as well as nectar. In so doing they may transfer 
some of the pollen from one flower to another of the same kind. 
This transfer of pollen, called cross-pollination, is of the greatest 
use to the plant, as we shall see later. Sir John Lubbock observed 
bees and wasps to learn how many trips they made daily from their 
homes to the flowers, and found that a wasp went out on 116 visits 
during a working day of 16 hours, while a bee made ^almost as 
many visits and worked almost as long as the wasp. It is evident 
that in the course of so many trips to the fields a bee must light 
on hundreds of flowers. 

Nectar and nectar glands. The bee is attracted to a flower for 
food. This food may consist of pollen or nectar. Nectar is a 
sugary solution that is formed in the flower by little collections 
of cells called the nectar glands. The nectar glands are usually 
so placed that to reach them the insect must first brush the stamens 
and pistil of the flower. Frequently the location of the nectaries 
(nectar glands) is made conspicuous by brightly colored markings 



ADAPTATIONS IN A BEE 



89 



on the corolla of the flower. The row of dots in the tiger lily is 
an example. 

Practical Exercise 11. Study a dead bee, to discover adaptations for 
carrying pollen. Use diagram in text to help. Hand lenses are essential 
and a compound microscope will be found useful. 

Adaptations in a bee. If we look closely at a bee, we find the 
body and legs more or less covered with tiny hairs, many of them 
branched. The joints in the legs of the bee adapt it for com- 
plicated movements; the arrangement of stiff hairs along the 
edge of a concavity in one of the joints of the hindmost pair forms 
a structure called the 
pollen basket, adapted 
to hold pollen. Bees 
collect pollen and force 
it into this concavity 
by means of a pollen 
press (usually called 
the wax shears), located 
between the two large 
joints of the hind pair 
of legs. Pollen ob- 
tained by the bee in 
this way is taken to 
the hive to be used as food. But while the insect is gathering 
pollen for itself, some is caught on the hairs and other projections 
on the body or legs and is carried from flower to flower (see page 72) . 

Field Exercise. In any locality where flowers are abundant, try 
to answer the following questions : How many bees visit the locality 
in ten minutes? How many other insects alight on the flowers? 
Do bees visit flowers of the same kind in succession, or fly from one 
flower on a given plant to another on a plant of a different kind? If 
the bee alights on a flower cluster, does it visit more than one flower in 
the same cluster? How does a bee alight? Exactly what does the 
bee do when it alights? Try to decide whether color or odor has the 
most effect in attracting bees to flowers. 

The cross-pollination of flowers is not planned by the bee ; it is 
simply an incident in the course of the food gathering. The bee 
visits a large number of flowers of the same species during the 




collection of 
pollen starts 

What part of the leg holds pollen ? 



aLthe return, 
to the Trtive 



Why! 



90 



HOW ARE ANIMALS AND PLANTS DEPENDENT? 



course of a single trip from the hive, and it is then that cross- 
pollination takes place. 

Other flower visitors. Other insects besides the bee are pollen- 
izing agents for flowers. Among the most useful are moths and 
butterflies. Both of these insects feed only on nectar, which they 
suck through a long tubelike proboscis. The heads and bodies 
of these insects are more or less thickly covered with hairs, and 
the wings are thatched with tiny hairlike scales. All these 
structures are of some use to the flower because they collect and 
carry pollen; but the palp, a fluffy structure projecting from 
each side of the head of a butterfly, collects a large amount of 
pollen, which is deposited upon the stigmas of other flowers when 
the butterfly pushes its head down into the flower tube after nectar. 

Flies and a few other insects are agents in cross-pollination. 
Humming birds are also active in pollinating some flowers. 
Snails are said in rare instances to carry pollen. Man and animals 
may pollinate a few flowers in brushing past them through the fields. 

Practical Exercise 12. Devise an experiment to determine if a given in- 
sect is attracted to a given flower by color or by odor. 

List in a table the plants in your neighborhood that are pollinated by butter- 
flies, bees, beetles, flies, bugs, or other insects. 



Butterflies 


Bees 


Beetles 


Flies 


Bugs 


Other Insects 















Self-Testing Exercise 

(1) is accomplished by the insect visitors to flowers. The 

chief adaptations in the bee for carrying pollen are the (2) on 

the legs and body. The bee uses pollen for (3) and carries it 

to the hive in (4) (5), concavities on the (6) 

pairoflegs (7), (8), (9),... (10), 

(11), and other animals may aid in cross-pollinating flowers. 

These animals visit flowers for (12) and not to (13) them. 



CROSS-POLLINATION 



91 



stigroct 
anther 

pollen. 



PROBLEM X. WHAT ARE SOME SPECIFIC EXAMPLES OF 
CROSS-POLLINATION ? 

Demonstration. Some of the material in the following paragraphs 
will be available for study. If possible, supplement the text with charts 
which can be used as a basis for discussion. Snapdragon may be sub- 
stituted for butter-and-eggs. 

Butter-and-eggs. From July to October in the East, the very 
abundant weed called " butter-and-eggs " may be found, especially 
along roadsides and in sunny fields. It bears a tall and con- 
spicuous cluster of yel- 
low and orange flowers 
known to botanists as 
a spike, the flowers 
being arranged so that 
they come out directly 
on main stalk. 

The corolla projects 
into a spur on the 
lower side; an upper 
two-parted lip shuts 
down upon a lower 
three-parted lip. The 
four stamens are in 
pairs, two long and 
two short. 

Certain parts of the 
corolla are more brightly colored than the rest of the flower. 
Butter-and-eggs is visited by bumblebees, which apparently 
are guided by the orange lip to alight just where they can 
push their way into the flower. The bee, seeking the nectar 
secreted in the spur, brushes its head and thorax against the 
stamens. It may then, as it pushes down after nectar, leave 
some pollen upon the pistil, thus effecting self-pollination. Later 
in visiting another flower of the same kind, the bee may leave 
some of the pollen of the first flower on the pistil of the second 
flower, thus causing cross-pollination. 




„nectccr 




By means of the text and diagram explain how the bee 
transfers pollen from one flower to another of " butter-and- 
eggs." 



92 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



stxgmct 
anther 




How does pollination take place in a daisy ' 



Cross-pollination of clover. In a clover head, which is a closely 

massed cluster of little flowers, cross-pollination is usually effected 
s by bumblebees which work 

rapidly from one flower to 
another in the same group, 
inserting their tongues deep 
into the flower cups. 

Cross-pollination of a 
composite head. The 
daisy, aster, and sunflower 
are examples of a com- 
posite head. The flower 
cluster has an outer circle 
of green parts which look 
like sepals, but in reality 
are a circle of leaflike 
parts. Taken together 

these form an involucre (in'v6-lu-ker). Inside the involucre is 

a whorl of brightly colored, irregular flowers called the ray flowers. 

They appear to act, in some instances at least, as an attraction to 

insects by showing a . , ^ 

definite color (see the 

common yellow A THlll \Y\Y P 

daisy). The flowers 

occupying the center 

of the cluster are the 

disk flowers. Pollen 

is carried easily from 

one flower to another 

even by an insect 

which crawls. 
Devices to secure 

cross-pollination. 

There are many other 

examples of adapta- 
tions to secure cross- 

,,. . , The length of the filaments and height of the stigma may make 

pollination by means the self -pollination of loose-strife impossible. Why ? 





SELF-POLLINATION 



93 



of the visits of insects. 
The mountain laurel 
shows a remarkable 
adaptation in having the 
anthers of the stamens 
caught in little pockets of 
the corolla. The weight 
of the visiting insect on 
the corolla releases the 
anther from the pocket in 
which it rests so that it 
springs up, dusting the 
body of the visitor with 
pollen. 

In some plants, self- 
pollination is prevented 
by certain devices, as in 
the primroses, in which 
the stamens and pistils 
are of different lengths in 
different flowers. Short 
styles and long filaments 
with high-placed anthers 
are found in some flowers, 
and long styles and short 
filaments with low-placed 
anthers in others. Polli- 
nation is most likely to be 
effected by some of the 
pollen from a low-placed 
anther reaching the stigma 
of a short-styled flower, or 
by the pollen from a high 
anther being placed upon 
a long-styled pistil. There 
are, as in the case of the 
spiked loose-strife, flowers 



EST •••*• 

.'■■■- 

■ 


%-' 






lf*::l 


«#r 




■ * . . ■■.>.-, 





Wright Pierce 

A species of yucca found in the Southwest. It is 
almost stemless, and has a stout flower stalk 12 to 15 
feet high carrying a cluster of fragrant, creamy white, 
bell-shaped flowers. 



94 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



motto. 



having pistils and stamens of three lengths. Pollen grows best 
on pistils of the same length as the stamens from which it came. 

The stamens and pistil ripen at dif- 
ferent times in some flowers. The 
" Lady Washington " geranium, a 
common house plant, shows this 
condition. 

Pollination of the yucca. A very 
remarkable instance of insect help is 
found in the pollination of yucca, a 
semitropical lily which lives in the 
washes and semi-desert regions in 
our Southwest. The anthers of this 
flower reach nowhere near the stigma, 
and the plant has to depend upon 
insects for fertilization. The insect 
which accomplishes this is the pro- 
nuba (pro'nu-bd) moth. The female 
moth gathers pollen from the anthers 
of these blossoms and shapes it into 
a pellet. She flies to another flower, 
and inserts her ovipositor into the 
ovary of the flowers and lays her eggs among the ovules. She 
then thrusts the pollen ball into the opening which extends the 
length of the style. When the egg hatches, the caterpillar feeds 
on some of the young seeds which have developed along with the 
larva. Later it bores its way out of the seed pod and escapes to 
the ground, leaving the plant to develop the remaining seeds 
without further molestation. 

How the fig is pollinated. The pollination of the fig is another 
wonderful example of adaptation. The fig is not a fruit but a 
cluster of fruits, growing inside the inturned ends of a fleshy 
flower stalk. There may be three kinds of flowers in the clusters, 
some bearing only stamens, some with only pistils with long 
styles, and others, pistils with short styles. Some fig flower 
clusters have long-styled pistillate flowers only, others contain 
both short-styled and staminate flowers, the latter above the 




The pollination of yucca. What is the 
moth doing in the lower figure ? 



POLLINATION BY THE WIND 



95 



pistillate flowers. All of these flowers are visited by a little wasp 
(Blastophaga grossorum). When it visits the short-styled and 
staminate fig, it lays its eggs in the ovary, which it can easily reach 
with its egg-depositing organ (the ovipositor) . The females which 
hatch work their way out and in doing so brush against the stami- 
nate flowers, thus collecting pollen on their bodies. They then 
seek other figs in order to lay their eggs. If a wasp reaches another 
short-styled flower cluster, the eggs are laid and development takes 
place as before. But if it flies to a long-styled cluster, it cannot 
reach the ovary to deposit its eggs. In both cases, however, the 
wasp has carried pollen to the stigma and pollination takes place 
with the subsequent development of seeds. The figs we eat are 
developed from the long-styled pistillate flowers. By importing 
the wasps to California it is possible to grow figs where for years 
it was believed that the climate prevented them from ripening. 

Pollination by the wind. Not all flowers are dependent upon 
insects for cross-pollination. Many of the earliest spring flowers 
appear almost before the in- 
sects do. In many trees, 
such as the oak, poplar, and 
maple, the flowers open be- 
fore the leaves come out. 
Such flowers are usually de- 
pendent upon the wind to 
carry the pollen from the 
stamens of one flower to the 
pistil of another. 

Among the adaptations 
that a wind-pollinated flower 
shows are : (1) The develop- 
ment of many pollen grains to 
each ovule. In flowers which 
are pollinated by the wind, a 
large number of the pollen 
grains never reach their des- 
tination and are wasted. Therefore thousands of 
must be formed to every ovule produced. 




A wind-pollinated flower. What devices are shown 
that aid in cross-pollination? 



pollen grains 



96 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



(2) The anthers are usually held high and exposed to the wind 
when ripe. The common plantain and timothy grass are excellent 
examples. 

(3) The pistil of the flower is peculiarly fitted to retain the pollen 
by having feathery projections along the sides which increase the 

surface of the stigma. 
^ All our grains, wheat, 

rye, oats, and others, 
have the typical 
feathery pistil of the 
wild grasses from which 
they have been de- 
veloped. 

(4) The corolla is 
often entirely lacking. 
It would only be in the 
way in flowers that are 
dependent upon the 
wind to carry pollen. 




becrrino 
pistillafe 



twfg 
stccm.ino.te- 



Why are the flowers of the willow imperfect ? Explain how 
cross-pollination might take place. 



easily accomplished by the wind 
Name a flower that has no corolla. 



stomi.ncLte-' fl&&r 

Practical Exercise 13. 

Name five plants that have 
a large proportion of pol- 
len grains to each flower. 
Study a diagram of a grass 
flower. Why is pollination 
What is the '''silk" of Indian corn? 
(Look up in a good botany.) 



Imperfect flowers. Some flowers, the wind-pollinated ones in 
particular, are imperfect ; that is, they lack either stamens or 
pistils. In such flowers, cross-pollination must of necessity be 
depended upon. In some trees, as the willow, staminate flowers 
(those which contain only stamens) are developed on one plant, 
and pistillate flowers (those which bear only pistils) on another. 
Other species have staminate and pistillate flowers on the same 
plant. The oak, hickory, beech, birch, walnut, and chestnut are 
familiar examples. 

Practical Exercise 14. Show by means of diagram how pollination might 
take place in the willow. 



TESTS 97 

Self-Testing Exercise 

Certain flowers, as butter-and-eggs, are especially fitted to receive 
(1), which cause both (2) and (3) pollina- 
tion. A composite head is composed of (4) and (5) 

flowers. Some flowers, as the yucca, are only pollinated when certain 

insects (6) their (7) in them and the seeds are 

(8) by the young parasites which hatch out. Self-pollination 

is usually impossible in flowers which have the (9) and 

(10) maturingat (11) times or placed on (12) 

flowers. Some plants have only (13) or (14) flowers 

and are pollinated by the (15). 

Review Summary 

Check your knowledge of the unit by (1) answering all survey questions; 
(2) performing all assigned exercises ; (3) checking with your teacher on all the 
tests and making up all incorrect work ; and finally (4) making an outline of 
the unit for your notebook. 

Test on Fundamental Concepts 

Make two vertical columns in your notebook, one headed CORRECT and the other IN- 
CORRECT. In one column write the numbers of the statements you believe to be true. In 
the other the statements you think are false. Your grade = correct answers times 2. 

I. All insects (1) have two pairs of wings; (2) have three body 
parts ; (3) have mouth parts adapted to chewing ; (4) have three pairs 
of legs ; (5) have an external skeleton of chitin. 

II. All insects breathe (6) through their wings ; (7) by taking air 
out of the water they drink; (8) through holes in the head; (9) by 
pumping air into their trachea; (10) by swallowing air. 

III. Insects may feed by (11) sucking through a proboscis, as the 
butterfly; (12) chewing by means of the mandibles, as the grass- 
hopper; (13) sucking through a beak, as the cicada; (14) lapping 
liquid food, as the beetle ; (15) piercing and sucking, as the bugs. 

IV. The life history of an insect may (16) have four different 
stages ; (17) be passed entirely underground as in the beetle ; (18) show 
an incomplete metamorphosis as in the grasshopper; (19) show a 
complete metamorphosis as in the house fly; (20) last for thirty or 
more years. 

V. Insects are very numerous because (21) they produce many 
young in a season ; (22) they may be colored like their surroundings 



98 HOW ARE ANIMALS AND PLANTS DEPENDENT? 

and thus avoid capture ; (23) they all taste badly to birds ; (24) many 
have a long quiescent period during metamorphosis ; (25) they have 
few enemies. 

VI. Insects when they visit flowers may (26) go there to lay their 
eggs; (27) carry pollen from one flower to another of a different 
kind; (28) pierce holes in the flowers in order to steal nectar; 

(29) transfer pollen from the anthers of one flower to the pistil of 
another flower of a different species, thus causing self-pollination; 

(30) carry pollen away without intending it, and thus cross-pollinate 
flowers. 

VII. Fertilization of a flower takes place when (31) a pollen tube 
is formed ; (32) an insect visits a flower ; (33) the sperm nucleus unites 
with the egg cell ; (34) pollen germinates on the stigma and grows a 
pollen tube ; (35) any two cells meet. 

VIII. Flowers have (36) essential organs called calyx and corolla ; 
(37) stamens, pistil, petals, and sepals; (38) structures called anthers, 
which produce pollen ; (39) organs called ovaries, which hold the egg 
cells ; (40) the possibility of producing seeds if they are pollinated. 

IX. Effective adaptations in insects for bringing about cross-pol- 
lination are: (41) hairs on the legs and body; (42) a long piercing 
beak ; (43) fluffy palps, as in the butterfly ; (44) smooth bodies, as in 
the ant ; (45) pollen baskets, as in the bee. 

X. The flowers most effectively adapted for bringing about cross- 
pollination are : (46) flowers with only stamens or pistils ; (47) flowers 
with essential organs of different lengths; (48) flowers having the 
stamens and pistils ripen at different times ; (49) showy flowers with- 
out essential organs; (50) flowers which prevent insect visitors from 
reaching the pollen. 

Achievement Test 

1. How can you tell an insect from other animals? 

2. Where would you look for the different orders of insects ? From 
how many of the orders of insects have you been able to find and 
collect representatives ? 

3. How many kinds of larvae and pupae in each of the above orders 
of insects can you name ? 

4. Have you ever studied an observation hive of bees ? Describe it. 

5. How could you make an artificial ant's nest and study the life 
of the colony? 



TESTS 99 

6. What are some examples of protective coloration or resemblance 
and warning coloration? 

7. What are the parts of a flower and the uses of each part? 

8. How would you germinate pollen grains in order to see a pollen 
tube? 

9. How would you make a diagram for your notebook that would 
describe fertilization in a flower? 

10. How can you show that a flower like the pea or apple blossom 
will form a fruit ? (Diagram for notebook.) 

11. What are all the adaptations in a bee for carrying pollen? In 
a butterfly? 

12. How can you distinguish between self-pollination and cross- 
pollination? 

13. How can you show by diagram the way in which a bee pollinates 
butter-and-eggs, clover, a daisy? (Draw diagrams in notebook.) 

14. How does cross-pollination in the yucca or the fig take placed 

15. How can you show that pollination takes place in (a) a chestnut 
or oak, (6) pine cone, (c) timothy grass ? 

Practical Problems 

1. Make a collection of insects and classify them according to the 
information given on pages 59-61. 

2. What insects are most abundant in your locality? How can 
you account for this? 

3. Select some flower and find out exactly how it is pollinated. 
Make diagrams to illustrate and explain your answer. 

Useful Books of Reference 

Coulter, Barnes, and Cowles, Botany. Volume Three, pp. 825-878. 

(American Book Company.) 
Downing, Our Living World. Chapters ii, iii, and vi. (Longmans, 

Green & Co. 1924.) 
Gager, General Botany. (P. Blakiston's Son & Co. 1926.) 
Luta, Field Book of Insects. (G. P. Putnam's Sons. 1921.) 
Palmer, Field Book of Nature Study. (Comstock Publishing Co. 

1927.) 
Transeau, General Botany. (World Book Co. 1923.) 




SURVEY QUESTIONS 

Why are weeds so plentiful? Why do weeds grow in places where 
other plants cannot exist? Do you know the common weeds in your 
locality and the ways to eradicate them ? Can you give a scientific defini- 
tion of a fruit ? Of what values are fruits to plants that produce them ? 



Photo by Wright Pierce 



UNIT IV 



HOW AND WHY DO SEED PLANTS SUCCEED IN LIFE? 



Preview. Our study will now be directed to two main problems ; 
first, what plants are most successful in their battle of life and, 
second, what fits them for this success. 

If you will go out any fall afternoon into the fields, a city park, 
or even a vacant lot, you can hardly escape seeing how seeds are 
scattered by the parent plants and trees. Several hundred little 
seedling trees may be counted under the shade of a single maple 
or oak tree. But nearly all these young trees are doomed to die, 
because of crowding and lack of sun. Plants, like animals, are 
dependent upon their surroundings for food and air. They need 
light even more than animals need it, because the soil directly 

100 



GROWTH OF WEEDS 101 

under the shade of a tree gives raw food material to the plants, 
and they must have sunlight in order to make it into food. Over- 
crowding is often seen in the garden where young beet or lettuce 
plants are growing. The gardener assists nature by thinning out 
the young plants so that they may not be handicapped in their 
battle for life by an insufficient supply of air, light, and food. 

It is evidently of considerable advantage to a plant to be able 
to place its progeny * at a considerable distance from itself, in order 
that the young plants may be provided with sufficient space to 
get nourishment and foothold. Some plants accomplish this, 
particularly weeds, more completely than others, and thus they 
are the more successful ones in the battle of life. Besides depriv- 
ing other plants of soil salts and water, weeds do much harm. 
Some are poisonous to cattle and sheep, as the loco-weed, hemlock, 
and laurel. Other weeds, as the wild onion or garlic, may be eaten 
by cows, and the milk produced will be ruined in flavor. Some 
weeds are hosts to injurious parasitic insects or fungi ; witness the 
Hessian fly, which lives in some wild grasses, and the wheat rust, 
which lives in the barberry. The pollen of the ragweed and of 
other weeds undoubtedly cause some people to have "hay fever." 

Weeds are introduced often into lawns and fields because their 
seeds are mixed with the good seeds which are sown there. We 
should use every method possible to prevent weeds from producing 
seeds. Poisons are used in some cases ; sheep, which seem to prefer 
some weeds to grass, are also a great aid in keeping down these 
pests ; and birds that eat weed seeds are the most valuable of all. 

PROBLEM I. WHAT ARE WEEDS AND WHAT DO THEY DO? 

Weeds are plants that grow in places where they are not wanted. 
They are generally stronger and faster growing than other plants 
and therefore they rob crops of food, moisture, and sunlight. 
Any vacant lot near the school will make a good laboratory for the 
study of weeds. In such an area we shall find numerous plants, 
many alike, and all growing closely together in soil that not infre- 
quently appears so dry and stony that it hardly seems possible 

1 Progeny (proj'e-nl) : offspring. 
B. BIO — 8 



102 



HOW DO SEED PLANTS SUCCEED IN LIFE? 



that plants could grow there. But weeds do grow and flourish 
under what seem impossible conditions for other plants. Let us 
see some reasons why. 

Laboratory Exercise. Visit a roadside, vacant lot, or meadow and 
observe the weeds growing there. Collect and, with the aid of one of 
the references given at the end of the unit, try to classify the various 
weeds growing in this area. Take one weed and study it carefully to 
determine why it is successful in surviving. Estimate the number of 
seeds produced, ways of scattering seeds, protection of seeds, and other 
adaptation of the plant to its environment, etc. 

Weeds produce many seeds. One fact readily observed is that 
many seeds are produced by weeds, be they daisies, dandelions, 
tumbleweeds, or ragweed. The table that follows shows approx- 
imately the number of seeds produced by an average sized plant. 
In your project on weeds, determine as accurately as possible the 
number of seeds produced by a plant and check the result against 
this table. 



Seeds Produced by a Sixgle Average-Sized Weed 



Dandelion . . 
Cocklebur . . 
Oxeyed daisy . 
Prickly lettuce 
Beggar ticks . 
Tumbleweed . 
Ragweed . . 



1,700 
9,700 
9.750 
10,000 
10.500 
14.000 
23.000 



Burdock . . 
Russian thistle 
Purslane . . 
Crab grass 
Willow foxtail 
Tumble mustard 
Worm seed 



24,500 

25,000 

69,000 

89,600 

113,600 

1,500,000 

26,000,000 



Individual Project. Make a collection of weed seeds, showing kinds 
and means of dispersal. 

Weeds have good methods of seed dispersal. We have all 
seen a dandelion or a thistle and know the feathery parachutes 
by which their seeds travel. Many of us have spent much time 
and energy in picking beggar-ticks or burdock burs from our 
clothes after a scramble through a weed-infested lot. Weed 
seeds or fruits may have hooks, prickles, fluffy outgrowths, or other 
appendages, which are used for carriage ; they may roll along the 
ground as the Russian thistle, or tumbleweed ; or they may have 
fruit that bursts when ripe, scattering their seeds. Some seeds have 



SEED DISPERSAL OF WEEDS 



103 



cork-like coverings and float long distances in streams. Birds 
eat some seeds and scatter them undigested, far from the parent 
plants. A study by some school children showed that common 
weeds given a start in one place might within three years, under 
average conditions, spread from an area four acres to over three 
hundred acres in extent around the point where they first came up. 
Why not make a study in your home locality to determine the 
rate of spread of some weed? 




Wright Pierce 

The Russian thistle, a tumbleweed, breaks loose when dry and is blown about by the wind, 
scattering its seeds as it rolls along. 

Laboratory Exercise. Select a common weed in your community, 
and bring it into the laboratory. Thrash out the seeds. Collect and 
count the seeds and estimate a possible total number of seeds which 
may be scattered over a given area by several hundred weeds. 

Weeds have great vitality. Those of us who have tried to get 
rid of weeds from a garden or from the lawn know some of the 
devices these pests have to maintain themselves : long and tough 
roots and stems ; roots which develop wherever the stem touches 
the ground; leaves protected by thorns or hairs; roots which 



104 



HOW DO SEED PLANTS SUCCEED IN LIFE? 



store food which help the plant to get a better start in the spring ; 
the ability to stand excessive heat and cold; and the ability to 
maintain themselves in wet or dry conditions. They often grow 
luxuriously under conditions that would kill an ordinary plant 
and grow so rapidly that they choke out their less favored com- 
petitors. Particularly, their seeds have great vitality, and may 

stay alive in the soil 
as long as twenty- 
five years after dis- 
persal from the 
parent plant. 

Practical Exercise 1. 

Find a number of dif- 
ferent ways in which 
weeds in your locality 
show vitality. 

Weeds have good 
methods of self- 
protection. Some 
structures by which 
weeds protect them- 
selves have already 
been noted, such as 
the hairs of the 
mullein or the prickly 
stem and the leaf of 
the thistle. Many 
grow low to the 
ground, as the dan- 
delion. Some are 
distasteful to ani- 
mals and others have a disagreeable odor, as the wild onion, tansy, 
or yarrow. Most weeds have the ability to resist disease and 
some, such as the dodder, are parasites and get their living from 
host plants, giving nothing in return. 

Individual Project. Collect and bring to class twenty-five common 
weeds. Mount them in passe-partout frames under glass. The col- 
lection will be of much value in weed identification. 




Department of Agriculture 



The field daisies are able to grow in poor soil and they are 
thus able to smother the useful plants. 



HARMFUL WEEDS 105 

Weeds grow where other plants cannot live. Many weeds, 
because of long roots and small leaf surface, are fitted to live where 
there is little water supply, or even in drought or desert condi- 
tions. Such are the Russian thistle, some of the true thistles, 
the poisonous loco weed, and our common ragweed. Many, at 
least when young, can get along in the shade of competing plants, 
their rapid growth enabling them to get into the sunlight later on. 
Such are the mustards which often color entire fields yellow with 
their tiny four-petaled flowers. Still other weeds seem to thrive 
under conditions of soil not suitable for other plants. Such are 
some of our desert and alkali-loving plants. 

Self-Testing Exercise 

Weeds are plants that (1) where they are not (2). 

They are usually (3) and (4) faster than agricultural 

plants. They rob crops of (5), (6), and (7). 

Weeds produce many (8). Weeds are plentiful because 

they have good methods of (9) (10), have great 

(11) and (12) where other plants cannot. 

PROBLEM II. WHY AND HOW SHOULD WEEDS BE 
ERADICATED? 

Harmful weeds. Weeds do harm in a number of ways. They 
reduce the farmer's crops tremendously. We have already seen 
that they force slower growing plants out. Think of the amount 
of productive labor lost through keeping weeds out of gardens and 
fields. Weeds are often introduced into fields through the mixing 
of their seeds with those of grains, or other crops bought for plant- 
ing. We can learn to identify such seeds under the microscope, 
and some farmers have such a test made to see if the seed they 
buy is pure. Weeds take the minerals and water from the soil 
much faster than the competing crops because they grow so 
quickly. Poisonous weeds, such as the loco weed, may kill or 
injure cattle. Some parasitic weeds like dodder, in the far West, 
kill great numbers of other plants. Another weed, the tall bar- 
berry, harbors another much more dangerous parasite, the wheat 
rust. Some wild grasses are inhabited by the pupae of the Hes- 



106 



HOW DO SEED PLANTS SUCCEED IN LIFE? 



sian fly, an enemy of the wheat plant. Ragweed and many others 
scatter pollen which causes hay fever to some people. 

Individual Project. Make a survey of your community or town 
for the tall barberry that harbors wheat rust. Destroy the barberry 
by. using either kerosene or rock salt on the ground over the roots. 

Poisonous weeds. Poison ivy, poison oak, and poison sumach 
cause very painful blisters to most people who touch them. Iron 
chloride is an excellent preventative, and in potassium permanga- 
nate dissolved in water is 
a standard relief agent. 

Poison ivy is an ex- 
ample of a weed that is 
extremely poisonous to 
touch. It is a climbing 
plant which attaches it- 
self to trees or walls by 
means of tiny air roots 
which grow out from 
the stem. It has leaves 
divided in three parts, 
which aid in distinguish- 
ing it from its harmless 
climbing neighbor, the 
Virginia creeper, which 
has leaves divided in five 
parts. Every boy and 
girl should know how 
poison ivy looks in order 
to avoid it. 

Numerous other poi- 
sonous common plants 
are found, one of which 
deserves special notice 
because of its presence 

L.W.Brownell in vacant C ity lots. The 

Above, poison ivy leaves. Below, leaves of Virginia , . . , 

creeper. How do they differ ? JlUlSOn Weed IS a DUShy 




POISONOUS WEEDS 



107 



plant, from two to five feet high, bearing large leaves. It has 
white or purplish flowers, and later bears a four-valved seed pod 
containing many hundred seeds. These plants contain a powerful 
poison, and children, through ignorance, are sometimes made 
seriously ill by eating the seeds or other parts. 




Wright Pierce 
A field of lupines. These are useful plants, as they give nitrogen to the soil. 

Useful weeds. Some weeds are not harmful, but are beautiful 
or useful in some ways. The daisy in New York, and the filaree in 
California, are dear to those who love flowers. Water cress, dande- 
lion, and some other weeds are used as food, and certain weeds are 
used for medicinal purposes. Plowed under they may act as 
fertilizer, and in some places they form a protective covering over 
the soil, thus preventing it from being washed away. 



Practical Exercise 2. 
in your community. 



Discuss the different methods of weed control used 



108 HOW DO SEED PLANTS SUCCEED IN LIFE? 

How may we eradicate weeds? We have seen the harm that 
weeds do. How can we get rid of them? The best way would 
be by not letting them get started. In the fall, burn over all lots 
that contain weeds. Prevent as many weeds as possible from 
producing seeds, especially those near gardens or fields of grain. 
This can be done by cutting the weeds before the seeds mature. 
Keep weeds out of roadside areas by early cutting. Since sheep 
like some kinds of weeds better than grass, they can be used in 
some localities to keep down the weeds. But in the main, de- 
stroying the weeds before they get a start seems to be the most 
effective means of ridding a place of them. 



Self-Testing Exercise 

Weeds are injurious to man because they (1) his crops. 

Some weeds may (2) cattle. Weeds harbor dangerous 

(3). Hay fever is caused by the pollen of (4). 

Wheat rust is a (5). Farmers often (6) weed 

seeds with (7). Weeds may be eradicated by (8), 

and (9) them before their seeds (10). Some weeds 

are (11) to (12), and some for (13). Poi- 
son ivy differs from Virginia creeper by having a leaf divided into 

(14) (15). Some poisonous weeds are (16) 

(17) and (18) (19). 



PROBLEM III. HOW ARE FRUITS AND SEEDS SCATTERED? 

Individual Project. Examine the fresh or preserved fruits of huckle- 
berry, blackberry, wild strawberry, wild cherry, black haw, wild grape, 
tomato, and currant. Report how many of the above have seeds with 
hard coatings. Notice that in most, if not in all, edible fruits the fruit 
remains green, sour, and inedible until the seeds are ripe. In the 
state of nature, how might this be of use to a plant? 

Adaptations for seed dispersal : fleshy fruits with hard seeds. 

Plants are fitted to scatter their seeds by special appendages or 
adaptations either in the fruit or in the seed. Various agents, 
as the wind, water, birds, and other animals, make it possible for 
the seeds to be taken away from the parent plant. 



DISPERSAL OF SEEDS 



109 



Fleshy fruits, that is, such fruits as contain considerable water 
when ripe, are eaten by animals and the seeds are passed off 
undigested. Most wild fleshy fruits have small, hard, indigestible 
seeds. Birds are responsible for scattering the seeds of many 
berries and other small fruit. Bears and other berry-eating ani- 
mals aid in this as well. Some seeds have especial adaptations 
in the way of spines or projections. Insects use these projections 
in order to carry them away. Ants plant seeds which they have 
carried to their nests for food supply. Nuts are sometimes planted 
by squirrels and blue jays. 

Hooks and spines. Some fruits which are dry and have a hard 
external covering when ripe possess hooks or spines which enable 
the whole fruit to catch in the coats of animals and are thus carried 
away from the parent plant. Thus the whole fruit cluster may be 
carried about and the seeds scattered. In many of the compos- 
ites, as in the cockleburs and beggar-ticks, the fruits are provided 
with strong curved projections which bear many smaller hooklike 
barbs. 

Pappus. The dandelion is an example of a plant in which the 
whole fruit is carried by the wind. The parachute, or pappus, is 
an outgrowth of the ovary 

wall. Many other fruits, no- llfw^ I"** 

tably that of the Canadian 
thistle, are provided with the 
pappus as a means of getting 
away from the parent plant. 
In the milkweed the seeds 
have developed a silky out- 
growth which carries them long 
distances from the parent plant. 

Dehiscent 1 fruits and how 
they scatter seeds. One of the 
many methods of scattering 
seeds is seen in dry fruits. 
These simply split to allow the escape of the seeds. Examples of 
common fruits that split open, called dehiscent fruits, are seen in the 

1 ^Dehiscent (de-Ms'ent) : opening along a definite line to discharge contents. 




.centfaei* 



Jxxppurs- 



-ovctry 



oc single 
/lower- 



How are the seeds of the Canadian thistle 
scattered ? 



110 



HOW DO SEED PLANTS SUCCEED IN LIFE? 



follicle (fol'i-k'l) of the milkweed, a fruit which splits along the 
edge of one valve, the pod or legume of the pea and the bean, and 
the capsule of Jimson weed and the evening primrose. The wild 
geranium, a capsule with five chambers, splits along the edge of 
each chamber, snaps back, and throws out the seed for some dis- 
tance. Jewel weed and witchhazel fruits burst open in a somewhat 
similar manner. 

Winged seeds. The seeds of the pine, held underneath the 
scales of the cone, are prolonged into wings which aid in their 

dispersal. The seeds 
of many of our trees 
are thus scattered. 

Other methpds. 
Sometimes whole 
plants as the tumble- 
weeds are carried by 
the high winds of the 
fall. Some seeds or 
fruits (for example, 
the coconut) may fall 
into the water and in 
a few days will be carried to a new place, the fibrous husk providing 
a boat in which the seed is carried. The seeds of swamp plants 
collect in the mud along the banks of ponds and streams, and birds 
which come there to feed carry them away on their feet. The 
great English naturalist, Charles Darwin, raised eighty-two plant's 
from seeds thus carried by birds. It is probable that most of 
the vegetation on the newly formed coral islands of the Pacific 
Ocean may have come from seeds brought to them by birds and 
by water. 

Practical Exercise 3. Name five fruits, other than those mentioned above, 
that scatter their seeds through the opening of pods. Name five trees that 
produce winged seeds. Why has the Russian thistle become a pest over such 
a large area in a relatively short time ? 

Indehiscent fruits. Dry fruits which do not split open to 
allow of the escape of their seeds are known as indehiscent fruits. 
Such are nuts, one-seeded fruits usually with hard outer covering, 




freexi pecc 

capsule, 

How are these particular fruits fitted for scattering their seeds ? 



STRUGGLE FOR EXISTENCE 111 

the so-called key fruits of the maple or ash, and many others. 
Corn, wheat, oats, etc., are indehiscent fruits. A grain is simply 
a one-seeded fruit in which the wall of the ovary has grown so 
close to that of the seed that they cannot be separated. Some 
indehiscent fruits are light and carried by the wind, others may 
be scattered by animals. 

Individual Project. Make a survey of your neighborhood to show 
at least some examples in every method of dispersal discussed in this 
unit. Make another classification of ways of dispersal, if you prefer. 

The struggle for existence. Those plants which provide best 
for their young are usually the most successful in life's race. 
Plants which combine with the ability to scatter many seeds over 
a wide territory, the additional characteristics of rapid growth, 
resistance to dangers of extreme cold or heat and to attacks of 
parasitic enemies, inedibility, and peculiar adaptations to cross- 
pollination or self-pollination, are usually called weeds. They 
flourish in the sterile soil of the roadside and in the fertile soil 
of the garden. By means of rapid growth they kill other plants 
of slower growth by usurping their territory. Slow-growing plants 
are thus actually exterminated. Many of our common weeds 
have been introduced from other countries and have, through their 
numerous adaptations, driven out other plants which stood in 
their way. Such is the Russian thistle. First introduced from 
Russia in 1873 in flaxseed, it spread so rapidly that it is now one 
of the greatest pests in our Northwest. Water cress, introduced 
in Australia by those who were fond of eating it in England, has 
become such a pest that it chokes navigable rivers and has to be 
dredged out frequently. 

Practical Exercise 4. Sum up all the ways in which weeds are successful 
in the struggle for existence. 

Self-Testing Exercise 

Seeds of fleshy fruits are scattered by (1). Animals 

scatter seeds that possess (2), or (3). The wind 

carries the seeds of (4), (5) (6), and 

(7) great distances. Another common agent for dispersing 



112 HOW DO SEED PLANTS SUCCEED IN LIFE? 

seeds is (8). The plants that (9) are those that 

scatter their (10) over a wide (11), grow (12), 

resist dangers of (13) and (14), and attacks of 

(15). 

Summary Outline 

Make an outline, similar to the ones you have used in the previous units. 
Fill it in for your notebook. Use it to make a summary recitation of the 
unit. Test your knowledge of the unit by (1) answering and rechecking the 
survey questions ; (2) performing correctly all assigned exercises ; (3) checking 
the answers to the various tests with your teacher and correcting all errors. 



Test on Fundamental Concepts 

Make two columns in your notebook, one headed CORRECT and the other INCORRECT. 
Place the numbers of the statements you think correct and incorrect under their respective 
columns. Your grade equals correct statements X 4. 

I. Weeds are abundant because (1) animals do not eat them; 
(2) they produce many and hardy seeds ; (3) they have many devices 
to scatter seeds ; (4) birds never eat their seeds ; (5) they can live in 
localities where other plants cannot exist. 

II. Weeds do harm because (6) they occupy the places that other 
plants might have in our gardens ; (7) they harbor dangerous para- 
sites; (8) some are poisonous; (9) sheep may eat them; (10) some 
cause disease, as hay fever. 

III. Weeds may be fought by (11) planting large areas to garden 
crops ; (12) burning over the infested areas ; (13) plowing them under 
in the fall; (14) having sheep feed on the infested area; (15) cutting 
them in the spring and early summer. 

IV. Seeds and fruits are scattered by (16) having fluffy outgrowths 
which carry them through the air; (17) having hooks or barbs; 
(18) splitting and letting the seeds out; (19) man; (20) rabbits and 
chickens. 

V. The most successful plants in the struggle for existence are those 
which (21) are able to scatter their seeds at a distance; (22) have 
been introduced where they have no natural enemies, as water cress 
in Australia; (23) grow faster than others which occupy the same 
area ; (24) are best fitted to endure unfavorable conditions ; (25) pro- 
duce few seeds. 



TESTS 113 

Achievement Test 

1. How can you identify 10 common weeds? 

2. How can you recognize poison ivy, poison oak, poison sumach ? 

3. What are the antidotes for these poisons? 

4. What are at least ten weed seeds ? 

5. What are five ways in which a weed scatters seeds? Scatters 
fruit? 

6. What are some fruits that are scattered in different ways? 

7. What are the best ways of controlling weeds in your locality? 

8. What, if any, weeds in your locality harbor dangerous parasites? 
If so, what have you done toward exterminating these enemies ? 

Practical Problems 

1. Make a weed garden, using a pocket germinator, and test which 
seeds germinate most quickly. 

2. Compare the number of seeds produced by some weed with that 
of some food-producing plant, as wheat. How do they compare? 

3. Make a list of all weeds eaten as food ; used as medicine. 

Useful References 

Atwood, Civic and Economic Biology. (P. Blakiston's Son & Co. 

1922.) 
Downing, Our Living World. (Longmans, Green & Co. 1924.) 
Georgia, Manual of Weeds. (The Macmillan Co. 1914.) 
Hodge, Nature Study and Life. (Ginn & Co.) 

The following pamphlets will be found very useful in helping to 
identify common weeds : 

Farmers Bulletin 86, 531, 660. 

U. S. Dept. of Agric. Bui. 28, Weeds and How to Kill Them. 

Bui. 161, Conn. Agric. Station (New Haven). 

Bui. 31, 70, Iowa Agric. Exp. Station (Ames). 

Bui. 50, 66, Kansas Agric. Station (Manhattan). 

Bui. 183, Kentucky Agric. Station (Lexington). 

Bui. 267, Michigan Agric. College Exp. Station. 

Bui. 62, North Dakota Agric. Station (Fargo). 

Bui. 59, Ohio Agric. Station (Wooster). 

Bui. 150, South Dakota Agric. Station (Brookings). 

Bui. 48, Univ. of Wise. Agric. Exp. Station (Madison). 




SURVEY QUESTIONS 

Do" plants need food? Can you tell what conditions are necessary for 
a seed to grow or germinate ? What causes an engine to move ? Could 
we say living things have to have fuel in order to work and live ? Do you 
know what has to happen to this fuel before it can be used ? Are there 
any differences between the way you and the seed make use of food? 



Photo by L. W. Brownell 



114 



PART II. GREEN PLANTS MAKE THE 
FOOD OF THE WORLD 

UNIT V 
WHY DO SEEDS GERMINATE? 

Preview. We have seen in a previous unit that the pollination 
of flowers usually results in the growth of a fruit containing 
seeds from which new plants grow. The purpose of the next 
few pages is to show how this baby plant, or embryo, grows into 
an adult. Every boy and girl knows that a dry seed, after lying 
dormant and apparently dead sometimes for months, will wake 
up and show signs of life when certain outside conditions are 
favorable. Evidently some conditions outside the seed start 
the growth of the little baby plant within the seed coats. There 
are several things which are absolutely necessary for germination, 
as this beginning of growth is called. The seed must first be pro- 
vided with a protective coat which keeps the delicate baby plant 
within from being harmed. Then it must be able to live for long 
periods under adverse conditions such as extreme dryness or lack 
of soil. Many seeds, especially those of weeds and some garden 
seeds, such as the radish, cabbage, carrot, cauliflower, cucumber, 
and turnip, may live for as long as ten years before being germi- 
nated, but the average age that a seed lives is much less than this. 
The stories of germinating of wheat found in the Tombs of the 
Pharaohs may be disbelieved, although recently some lotus seeds, 
believed to be at least four hundred years old, were taken from a 
dried lake bed in the Gobi Desert, and were successfully germi- 
nated. But the reason that these seeds retained their vitality was 
because they were protected from decay by the peat bog in which 
they were embedded. 

115 



116 WHY DO SEEDS GERMINATE? 

Two sets of factors are necessary for the growth of seeds: 
first, the presence of food substances inside the seed in order to 
give the baby plant a start in life ; and, secondly, certain stimulat- 
ing factors outside the seed, such as air, moisture, and warmth. 
Experiments which you can do yourself and observations you can 
make in almost any garden show the necessity of these factors 
very clearly. One value you will get from this unit will be the 
opportunity you have for determining, by means of certain simple 
experiments, the factors which control the beginnings of growth 
in a seed. 

It is a trite but true saying that we grow because we use food. 
The same is true of plants. Certain food substances, the organic 
nutrients (such as carbohydrates, fats, and proteins), are found 
in seeds. We eat peas and beans. If we test these seeds, we can 
show the presence of foodstuffs within them. The pea or bean 
seedling uses the locked-up energy within the foods in order to 
break out of the seed coat and force their growing roots and stems 
through the soil. The little plants also grow in size. This indi- 
cates quite clearly that some of the nutrients within the seed are 
transformed in some mysterious manner into the living material 
out of which the plant is built. Later we shall be able to make a 
comparison of the manner in which these nutrients are used by the 
plant with the way in which we use these same food substances. 
It will be sufficient to say here that the foods which are really 
outside of the baby plant must be changed from a solid food sub- 
stance into a liquid form so that the cells out of which it is formed 
may absorb the food substances into their own bodies. This 
process of changing insoluble foods into soluble food substances 
is called digestion. 

PROBLEM I. WHERE ARE BABY PLANTS FOUND? 

Laboratory Exercise. Make a drawing of a bean pod. Mark all 
the parts of the flower that you can find in it. What is a pod? Now 
open the pod and examine the seeds. How are they attached? 
Remove a bean, open it, and find the tiny future stem and leaves of 
the baby plant between the two " halves " of the bean called the 
cotyledons. Referring to the next paragraph, draw and label all the 
parts of the bean seed. 



THE BEAN 



117 



The bean. If we open a bean pod, we find the seeds lying 
along one edge of the pod, each one attached to the inner wall at 
the placenta by a little stalk through which it gets its nourishment. 




remains of stigma 
_..seecL 



-.-plctCenbcx 



..Valve of pod 



The stalk leaves a scar on 
the coat of the bean, called 
the hilum (hi'tam). The 
tiny hole near the hilum 
is the micropyle (mi'krO- 
pil). Turn to the diagram 
on page 85, showing the 
fertilization of an ovule. 
Find there the little hole 
through which the pollen 
tube reached the embryo 
sac. This small structure, 
the micropyle, remains 
and is found in the seed. 
The thick seed coat, the 
testa, is readily removed 
from a soaked bean. The 
seed then separates into 
two parts : the cotyledons 
or seed leaves. The rodlike part between the cotyledons is called 
the hypocotyl (hl'pS-kot'il) . This will later form the root and 
part of the stem of the young bean plant. The first true leaves, 
very tiny structures, are folded together between the cotyledons, 
and, with the future stem, are known as the plumule (ploo'miil). 
All the parts of the seed within the seed coats form the embryo 
or young plant. A bean seed contains, then, a tiny plant pro- 
tected by a tough coat. 

Practical Exercise 1. Using a number of seeds, show to the class the pres- 
ence of an embryo in each. Does it occupy the same position in each case? 
Write in your notebook a good definition of a seed. 

Food in the cotyledons. The laboratory work shows us that 

a seed really contains a baby plant or embryo, with a sufficient 

supply of food to give it a start in life. The problem now before 

us is to find out how the embryo of the bean is adapted to grow 

H. bio — 9 



A pod opened to show attachment of seeds, 
the parts of the flowers. 



Find 



118 



WHY DO SEEDS GERMINATE? 



into an adult plant. Up to this stage of its existence it has had 
the advantage of food and protection from the parent plant. Now 
it must begin the battle of life alone. We shall find in all our work 
with plants and animals that the problem of food supply is one 
of the most important problems to be solved by the growing 
organism. Let us see if the embryo is able to get a start in life 
(which many animals get in the egg) from food provided for it 
within its own body. 

Self-Testing Exercise 

The bean pod contains (1) which under favorable condi- 
tions will (2). The (3) is the baby plant within the 

(4). Its parts are the (5), the (6), and 

the (7). The (8) contain the food supply for the 

(9). 



PROBLEM n. WHAT ARE THE TESTS FOR THE ORGANIC 
NUTRIENTS FOUND IN SEEDS? 

Demonstration 1. Test for starch. Boil water with some laundry 
starch in a test tube, then cool it, and add to the mixture two or three 

drops of iodine 1 solu- 
tion. The mixture in 
the test tube turns 
purple or deep blue. 
It has been learned 
after many experi- 
ments that starch is 
turned purple or 
dark blue by iodine. 
Therefore, iodine so- 
lution is used as a 
test for the presence of 
starch. 

Demonstration 2. 
Test for oils. If a 
substance is rubbed 
on brown paper or is 
placed on paper and 
then warmed in an 
oven, the presence of 

1 Iodine solution is made by simply adding a few crystals of iodine to 95 per cent 
alcohol ; or, better, take by weight 1 gram of iodine crystals, f gram of iodide of 
potassium, and dilute to a dark brown color in weak alcohol (35 per cent) or dis- 
tilled water. 



diluted: 
starch 
-paste.. 




NUTRIENTS IN THE BEAN 



119 



vhite 
of egg 
in 
solution. 



<J 



nitric 
+acicl 
and 
heat 









oil will be shown by a translucent spot on the paper. Since the propor- 
tion of oil in beans is small, it is better to try this test with a walnut. 

Demonstration 3. Test for protein. Another nutrient present 
in the bean cotyledon 
is protein. Several 
tests are used to de- 
tect the presence of 
this nutrient. The 
following is one of the 
best known : 

Place in a test tube 
a bit of hard-boiled 
white of egg. Pour 
over it an 80 per cent 
nitric acid, and heat 
the tube gently. Note 
the color that ap- 
pears — a lemon yel- 
low. If a little am- 
monium hydroxide is 
added, the color turns 
a deep orange. 



Cool, 

4-acCdin 

excess, 

ammonia^ 



.starch grain 



A-ceIl*wtdl 



Practical Exercise 2. Test a number of substances for the presence of 
starch, fat, and protein. Give your findings in tabular form. What is the 
value of knowing these tests ? 

Nutrients in the bean. If we mash up a small piece of a bean 
cotyledon which has been previously soaked in water, and test it 
with iodine solution, the characteristic blue-black color appears, 
showing the presence of starch. If a little of the stained material 

is mounted in water on a glass slide 
under the compound microscope, we 
shall find that the starch is in the 
form of little ovoid bodies called 
starch grains. The starch grains and 
other food products are made use of 
by the embryo. 

A test of the cotyledon of a bean 
with nitric acid and ammonium 
hydrate shows us the presence of 
protein. Beans are found by many 
tests to contain about 23 per cent of protein, 59 per cent of 
carbohydrates, and 2 per cent of oils. The young plant within 




protoplasm. 



Cells from a potato, under microscope. 
Which part of the cell turns blue with 
iodine? 



120 WHY DO SEEDS GERMINATE? 

a bean is thus shown to be well supplied with nourishment until 
it is able to take care of itself. In this respect it is somewhat like 
a young animal within the egg, such as a bird or fish. All of our 
cereal foods are made from seeds or grains that contain proteins, 
carbohydrates, and oils. Seeds also contain water and mineral 
matter, as can be shown by simple experiments. 

Self-Testing Exercise 

(1) solution is used to (2) for the presence of 

starch. If the (3) tested turns dark (4) or (5) > 

we know that starch is present. Oil is known by the presence of a 

(6) spot when the (7) is heated on (8). To 

test for protein we add (9) (10) to the substance : if 

it turns (11) (12), it is an indication that (13) 

is present. If (14) (15) is then added to the sub- 
stance and it turns a deep (16) color, we may be sure that 

it is a protein. 

PROBLEM III. WHAT FACTORS ARE NECESSARY TO 
AWAKEN THE EMBRYO WITHIN THE SEED? 

Demonstration 4. To show how much water is needed for the 
germinating of peas. 

Materials. Soaked and dry peas, sawdust, cups. 

Method. Place an equal amount of moist sawdust in the bottom of 
each of two cups. 1 Put ten soaked peas in each. In a third cup con- 
taining dry sawdust put ten dry peas. Keep the seeds in one cup 
partially covered with water, those in the second slightly moistened, and 
those in the third dry. Keep the cups covered in a moderately warm 
place. Examine them daily for four days. Tabulate your results. 

Conclusion. Which amount of water seems best for germination ? 
Give your reasons. 

How much water does a seed need in order to germinate? 

The exact amount of water which is most favorable for the ger- 
mination of a seed can be determined only by careful experiment. 

1 Pupils performing this or any other experiments must remember that the suc- 
cess of an experiment depends upon the accuracy with which it is performed and 
the exclusion of all factors from the experiment except the one which they are try- 
ing to prove. For example, in the experiment on the effect of different amounts of 
moisture, all the other factors — temperature, light, food, etc. — must be the same 
in each of the three cups ; the only variable factor being moisture. 



TEMPERATURE FOR GROWING SEEDS 121 

An oversupply of water may prevent growth of seeds almost as 
effectually as no water at all. In general the amount most favor- 
able for germination is a moderate supply. Seeds rapidly lose 
their vitality if kept in a very moist atmosphere, especially if the 
moist air is hot. If seeds are given too much water they drown. 

Demonstration 5. To show the best temperature for germinating 
peas. 

Materials. Soaked peas, sawdust, boxes. 

Method. Plant twenty soaked peas in each of three boxes containing 
moist sawdust. Put one box in a place where the temperature is 
about 150° F., another where the temperature is about 70° F., and the 
third where the temperature is about 40° F. Give to all the same con- 
ditions of air, light, and moisture. Observe them for four days. 
Tabulate the daily observations. 

Conclusion. State what temperature seems best for germinating 
peas. Give reasons. 

What is the best temperature for germinating seeds? Here 
again our experiment answers the question only for the seed with 
which we are working. Peas germinate best at one temperature, 
corn another, wheat still another — or more properly, each variety 
of a seed has a certain temperature (called its optimum) at which 
it germinates best. It is this fact that makes possible the earlier 
germination of some garden seeds. 

Demonstration 6. To show that air is necessary for germinating 
peas. 

Materials. Soaked peas, bottles, sawdust. 

Method. Place an equal amount of moist sawdust in the bottom of 
two bottles. Fill one bottle full of peas and close it securely with a 
stopper. Put about twenty peas in the bottom of the other bottle. 
Examine the bottles daily for four days. 

Conclusion. In which bottle did germination take place ? Why? 

Why is air necessary for germination ? All living things respire 
or use oxygen in order to release energy and a seed is no exception 
to the general rule. Without an ample supply of oxygen it 
cannot release from its food supply the energy necessary for its 
growth. Hence a constant supply of fresh air is an important 
factor in the germination of seeds. If the seeds are planted in the 
ground it is necessary for the soil to be sufficiently loose so that 
air can penetrate it. 



122 WHY DO SEEDS GERMINATE? 

Self-Testing Exercise 

In order for seeds to germinate they need a (1) supply of 

(2), a certain degree of (3), and (4). The 

amount of (5) required for germination varies with the kind 

of ;. . (6). If too much (7) is used, some seeds will 

(8) or decay. 



PROBLEM IV. WHAT BECOMES OF THE PARTS OF THE 
EMBRYO DURING ITS GROWTH INTO A YOUNG PLANT? 

Germination. If you plant a number of soaked kidney beans 
in damp soil or sawdust and at the end of each day remove one, 
you will be able to obtain a complete record of the growth of the' 
kidney bean. The first signs of germination are the breaking of 




Stages in the growth of a bean. Note the direction of growth in the root. How does the cotyle- 
don get out of the ground ? What has happened to the hypocotyl in the right-hand figure ? 

the testa and the pushing outward of the hypocotyl to form the 
first root which grows downward. A later stage shows the 
hypocotyl forming an arch and dragging the bulky cotyledons 
after it. The stem, as soon as it is released from the ground, 
straightens up. The cotyledons open, and between them the 



GERMINATION 123 

budlike plumule grows upward, forming the first true leaves and 
all of the stem above the cotyledons. As growth continues, we 
notice that the cotyledons become smaller and smaller, until their 
food contents are completely absorbed by the young plant. The 
young plant now has roots and leaves and is able to care for itself 
and may be said to have passed through the stages of germination. 

Laboratory Exercise. Examine several stages in the growth of the 
pea or bean. Make drawings for your workbook to illustrate at least 
three of the stages described below. 

Practical Exercise 3. Look up in seed catalogs or gardening books how 
deep you should plant several different kinds of seeds. Is there any relation 
between the depth of planting and the size of the seed? If so, explain this. 

Self-Testing Exercise 

When a bean seed germinates, the (1) first grows (2). 

Then it develops an (3) which draws up the (4) as it 

grows upward. Later the (5) develops. During this growth the 

(6) are used up as (7) by the (8) (9) . 



PROBLEM V. WHAT MAKES A YOUNG PLANT GROW? 

Demonstration 7. To prove that growing seeds oxidize food. 

Materials. Bottle, rubber stopper, thistle tube, delivery tube, soaked 
peas, blotting paper, and limewater. 

Method. Put some soaked peas in the bottom of a bottle containing 
some soaked blotting paper. Fit the bottle with a rubber stopper con- 
taining a thistle tube and a delivery tube. 

_ Watch for evidences of growth in the bottle. At the end of forty- 
eight hours, insert the delivery tube in a tube of limewater. Pour 
water through the thistle tube into the bottle. What happens to the 
limewater ? Why was water poured through the thistle tube ? 

Conclusions. Remembering what you have learned in your previous 
experiments, account for what happened. Why did the seeds start 
to grow? From what source did the seeds get their energy to grow? 

Write a brief statement, using proof to show that energy is stored 
in food and that it can be released and used only by oxidation. 

What makes an engine go. If we examine the sawdust or soil 
in which the seeds are growing, we find it forced up by the growing 
seeds. Evidently work was done; in other words, energy was 



124 



WHY DO SEEDS GERMINATE? 



released by the seeds. A familiar example of release of en- 
ergy is seen in an engine. Coal is placed in the fire box and 
lighted, and the lower door of the furnace is opened so as to 



y. .stopper 




equal number of £ eects im-s 
A fi^d. B 

Why is the growth of seeds in flask B greater than 
that in flask A ? 



make a draft of air which 
will reach the coal. The 
coal burns, heat is released, 
causing the water in the 
boiler to make steam, the 
engine wheels to turn, 
and work is accomplished. 
Let us see what happens 
from the chemical stand- 
point. 

Coal is formed largely 
from dead plants, which 
were long ago pressed into 
the present hard form of 
coal. It contains a large amount of the chemical element carbon. 
We have already observed one of the effects of the oxidation of 
carbon as proved by the lime water test. Let us now apply this 
test to the oxidation of food substances in our own bodies. 

Demonstration 8. To prove that food materials are oxidized by the 
human body. Expel air from the lungs through a tube into a bottle 
of lime water. Note what happens. As a control pass air from the 
room through lime water. Explain your results. 

Oxidation in our bodies. In life the temperature of the body 
(98.6° Fahrenheit) is due to oxidation within the cells. Food is 
also oxidized within the human body to release energy for our 
daily work. In fact, all living things, both plant and animal, 
release energy as the result of oxidation of food within their cells. 



Self-Testing Exercise 

The presence of (1) (2) in large amounts in the air 

surrounding seeds growing in a closed jar indicates that they have 

(3) food within their bodies. The (4) of (5) 

in the body releases (6) to do work. When seeds grow they take 

in (7) and give off ........ (8) (9), 



ENDOSPERM IN SEEDS 



125 



PROBLEM VI. WHERE IS THE FOOD SUPPLY OF DIFFERENT 

SEEDS? 

Laboratory Exercise. To study the structure and composition of 
a grain of corn. 

Materials. Soak corn grains, some whole and some cut lengthwise 
at right angles to the flat surface. 

Method and Observations. In whole corn grain find a light-colored 
area on one side. This marks the position of the embryo. 

In a grain cut lengthwise at right angles to the flat side find the 
embryo. Describe its shape, position, and relative size compared 
with the rest of the corn grain. The area outside of the embryo is 
known as the endosperm. Place iodine on the surface of the cut 
corn grain. Describe what happens. Test a grain of corn for protein. 

Conclusion. What nutrients are present in the corn? Where are 
they found? 

Endosperm the food supply of corn. We find that the one 
cotyledon of the corn grain does not serve the same purpose to the 
young plant as do the two cotyle- 
dons of the bean. Although we 
find a little starch in the corn 
cotyledon, still it is evident from 
our tests that the endosperm is the 
chief source of food supply. The 
study of a thin section of the corn 
grain under the compound micro- 
scope shows us that the starch 
grains in the endosperm are large 
and regular in size. When the 
embryo has grown a little, an ex- 
amination shows that the starch 
grains near the edge of the cotyle- 
don are much smaller and quite 
irregular, having large holes in 
them. This means that the starch 
is being used by the young plant. 

Seeds with endosperm. In the 
seeds of the pea and bean we have found that the embryo takes 
up all the space within the seed coats. There are some plants 
that have food stored outside of the embryo. Such a plant is the 




Wi 



endosperm 



tA^l edbn, 



-plumule. 



--WpoCotyl 
root^tAp 



Longitudinal section of a grain of corn. 
Find the embryo. Is the corn a seed or 
a fruit? Why? 



126 



WHY DO SEEDS GERMINATE? 



castor bean. A section cut vertically through the castor bean 
discloses a white oily mass directly under the seed coats. This 
mass is called the endosperm. If it is tested with iodine, it will be 

found to contain 




.testa.. 



cot- 




starch; oil is also 
present in consid- 
erable quantity. 
Within the endo- 
sperm lies the em- 
y^^&^ bl T > a thin > whitish 

asparagus "pine-- castor bean. "peanut structure. 

Seeds always contain a food supply which may be either in the coty- JYLOnOCOtyleClOnS > 
ledons of the embryo or in an endosperm outside of the embryo. dicotvledotlS and 

polycotyledons. Plants that bear seeds having but a single cotyle- 
don in the embryo are called monocotyledons. Although we find 
many monocotyledonous plants in this part of the world, the group 
may be said to be characteristic of the tropics. Sugar cane and 
many of the large trees, such as the date palm, palmetto, and 
banana, are examples. Among the common monocotyledons of 
the north temperate zone are corn, lilies, grasses, grains, and 
asparagus. 

Dicotyledons, or plants having two cotyledons in the seed, are 
those with which we come in contact most frequently in daily 
life. Many of our garden vegetables, peas, beans, squashes, 
melons, etc., all of our great hardwood forest trees, beech, oak, 
birch, chestnut, and hickory, the shade trees of our city streets, 
elm, maple and poplar, all of our fruit trees, pears, apples, peaches, 
and plums, and, in fact, a very large proportion of all plants 
living in the north temperate zone, are dicotyledons. 

A third type of plant, with more than two cotyledons, is the 
group called the polycotyledons, represented by the pines and their 
kin. Such plants furnish most of the lumber and shingles used 
in the construction of frame houses. The soft woods, as the pines, 
hemlocks, spruces, and other " evergreens," are also of much 
value in the manufacture of paper. The wood-pulp industry has 
grown to such proportions as to be a menace to our softwood 
forests. 



SELF-TESTING EXERCISE 



127 







Brooklyn Botanical Garden, Brooklyn, N. Y. 
The upper picture shows date palms growing in Algeria ; the lower left shows a white oak 
tree ; and the lower right shows a white pine tree. Why are these trees classified as mono- 
cotyledons, dicotyledons, and polycotyledons respectively. 

Self-Testing Exercise 

Seed plants are divided into three groups : (1), (2), 

and (3). In the first, the food is stored in the (4), 

while in the second group it is in the (5). Corn is a (6), 

while the bean is a (7). The pine is an example of a 

(8). 



128 WHY DO SEEDS GERMINATE? 

PROBLEM VII. HOW DOES THE CORN GRAIN MAKE USE 
OF STORED FOOD? 

Demonstration 9. How is the endosperm used ? 

Remove the endosperm from some corn grains that have just started 
to sprout. Place them in moist sawdust side by side with some normal 
sprouted grains. Give each lot of seedlings the same conditions of 
water, light, and air. 

Watch them carefully for at least two weeks. What differences do 
you observe in the rates of growth in the two lots of seedlings ? 

Conclusion. What is the relation of the endosperm to growth? 

Changes in the food supply of a seed during germination. We 

have learned that the chief source of the food supply of the corn 
grain is the endosperm which contains starch and also some pro- 
tein in its outer parts. These foods are in an insoluble form. In 
order that the growing embryo may make use of the stored nutri- 
ents they must be changed into a soluble form so that they may 
be carried out of the endosperm through the cotyledon to the 
growing parts of the embryo. Starch can easily be changed by 
the process of digestion into grape sugar or glucose 1 which is 
soluble. We know that the germinating corn grain has a sweeter 
taste than that which is not growing. This is noticed also in 
sprouting barley or malt. The germinating grain contains grape 
sugar which has been formed from the starch. This, with protein 
which has also been digested in the endosperm, passes from cell 
to cell and thus reaches the growing part of the embryo. 

This process of chemical change- or digestion cannot take place 
in dry seeds. Water must be absorbed by the seed, first, in order 
to allow digestion to take place and, second, to allow the soluble 
material to dissolve and pass through the cells. This digestion 
cannot take place without a moderate degree of warmth. For 
this reason moisture and warmth are necessary for germination. 

Test for grape sugar. Just after the test for starch was worked 
out, a chemist by the name of Fehling prepared a solution which 
is named in honor of him and which is used as a test for glucose. 
An American chemist, Dr. Benedict, modified this solution and we 
can now use either the Fehling or the Benedict solution as a test 
for glucose. 

1 Grape sugar, or glucose, is a simple kind of sugar found in many plants and is 
the form in which digested starch is passed on to the plant cells. 



DIGESTIONS 129 

Demonstration 10. To show the test for grape sugar. 

Materials. Glucose, Fehling's or Benedict's solution, 1 test tubes, 
Bunsen burner. 

Method. Place in a test tube a little glucose and water. Add to it 
an equal volume of Fehling's solution. Heat the mixture to the boiling 
point. 

If the color of the mixture becomes brick red after heating a short 
time with Fehling's solution, chen grape sugar is present, a precipitate 
will be formed having a red, yellow, or green color, depending upon the 
amount of sugar present. 

Conclusion. Is Fehling's solution a test for cane sugar? Explain. 

Laboratory Exercise. Wash some dry, unsprouted corn grains and 
test them for grape sugar. Then cut some corn grains that have just 
begun to germinate, lengthwise, through the embryo, and test for 
grape sugar. Look for changes in color between the embryo and 
endosperm. 

Using a diagram, fill in with correct colors the changes that took 
place when germinating corn was tested. 

Digestion. The change of starch to grape sugar in the corn 
is due to a process called digestion. If you chew for a little time 
a bit of unsweetened cracker — which we know contains starch — 
it will begin to taste sweet, and if the chewed cracker is tested with 
Fehling's solution, some of the starch will be found to have changed 
to grape sugar. Here, again, the process of digestion has taken 
place. Both in the corn and in the mouth, this change is brought 
about by the action of chemical substances known as digestive 
ferments, or enzymes (en'zlmz). Such substances have the power 

1 Fehling's solution may be made as follows : Add 35 g. of copper sulphate to 
500 cc. of water. Solution No. 1. 

To 160 g. caustic soda (sodium hydroxide) and 173 g. Rochelle salt, add 500 cc. 
of water. Solution No. 2. 

For use mix equal parts of solutions 1 and 2. This may also be obtained from 
druggists, in tablets. 

Benedict's second solution. — Copper sulphate ........ 17.3 g. 

Sodium citrate 173.0 g. 

Sodium carbonate (anhydrous) . . . 100.0 g. 

Make up to 1 liter with distilled water. 

With the aid of heat dissolve the sodium salts in about 600 cc. of water. Pour 
through filter paper into a glass graduate and make up to 850 cc. with distilled 
water. 

Dissolve the copper sulphate in about 100 cc. of water, and make up to 150 cc. 
with distilled water. Pour the carbonate citrate solution into a large beaker and 
add the copper sulphate solution slowly with constant stirring. 

— After Hawke's Biochemistry. 



130 



WHY DO SEEDS GERMINATE? 



equal 

volumes 

of grape 

sugar* 

and. 

TehWnds 

solution. 



4. heat,^ 



\J 



under certain conditions to change insoluble foods — solids — 
into soluble substances. The result is that foods which before 

digestion would not dissolve in 
water will dissolve after being 
digested. 

The action of diastase on 
starch. The enzyme found in 
the cotyledon of the corn, which 
changes starch to grape sugar, 
is called diastase (di'd-stas). It 
may be separated from the 
cotyledon and is prepared by 
chemists for use in the form of 
a powder. 



Explain what has happened here, 
it show? 



What does 



Demonstration 11. To show 
how starch is changed to sugar. 

To a little starch in half a cup of 
water add a very little diastase 
(1 gram) and put the vessel containing the mixture where the tempera- 
ture will remain nearly constant at about 98° Fahrenheit. Test part 
of the contents at the end of half an hour, for starch and for grape 
sugar. If the rest of the mixture is tested the next morning, it will 
be found that the starch has been completely changed to grape sugar. 
Starch and warm water alone under similar conditions will not react 
to the test for grape sugar. 

Digestion has the same purpose in plants and animals. In 

our own bodies we know that solid foods taken into the mouth are 
broken up by the teeth and moistened by saliva. If we could 
follow that food, we should find that eventually it became part of 
the blood. It was made soluble by digestion, and in a liquid form 
was absorbed into the blood. Once a part of the body, the food is 
used either to release energy or to build up the body. 



Self-Testing Exercise 

Check correct answers for your workbook. 

Digestion is brought about by: (1) heating the food in the body; 
(2) chewing the food well ; (3) enzymes ; (4) adding grape sugar to a 
substance. 



REVIEW SUMMARY 131 

A SUMMARY OF FOOD SUBSTANCES AND THEIR TESTS 



Name 


Chemical Compositiox 


Test 


Starch 


Contains Carbon (C) 

Hydrogen (H) 
Oxygen (0) 


Solution of iodine turns it dark 
blue. 


Grape sugar 


Contains Carbon (C) 

Hydrogen (H) 
Oxygen (0) 


Forms brick-red precipitate 

when heated to boiling with 

Fehling's solution. 
Forms greenish, yellow, or red 

precipitate when boiled with 

Benedict's solution. 


Fats and oils 


Contain Carbon (C) 

Hydrogen (H) 
Oxygen (0) 


Leave a grease spot on paper 

after heating. 
May be extracted by mashing 

up substance with ether. 


Proteins 


Contain Carbon (C) 

Hydrogen (H) 
Oxygen (0) 
Nitrogen (N) 
and usually Sulphur (S) 
and other elements 


Turn yellow when heated with 
strong nitric acid, and then 
turn orange after addition 
of ammonium hydroxide 


Burning test (odor) 
Coagulation test (white of egg) 


Mineral matter 


Such elements as Sodium 
(Na), Calcium (Ca), 
Iron (Fe), and Potas- 
sium (K) 


Remains as grayish ash after 
burning food in hot flame for 
long period. 


Water 


Hydrogen (H) 
Oxygen (0) 


Passes off from food when 
heated, as water vapor, and 
can be collected on cold 
metal or glass, as drops of 
water. • 



Digestion is necessary for plants and animals because : (1) it gives 
them the nutritious part of their food ; (2) it breaks food into small 
particles; (3) it releases energy in foods; (4) it makes substances 
soluble. 

Review Summary 

Test your knowledge of the unit by: (1) Answering and rechecking the 
survey questions ; (2) performing the assigned exercises ; (3) checking with 
the teacher, your scores on the various tests, and if you do not have a perfect 
score trying again the parts you missed ; and finally, (4) making an outline 
and filling it in as fully as possible for your notebook. 



132 WHY DO SEEDS GERMINATE? 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 4. 

I. An embryo (1) is found in all seeds; (2) is a young plant; 
(3) will not be formed unless the flower has been pollinated; (4) in 
the bean consists of the testa and plumule ; (5) is the part of the seed 
that grows into a young plant. 

II. Among the factors necessary for germinating seeds are: 
(6) food but no water; (7) light; (8) air, water, heat, and food; 
(9) a temperature of 100° or over; (10) rich soil and an abundance of 
water. 

III. Organic foods (11) are found in the cotyledons of the bean; 
(12) are stored in the cotyledon of the corn; (13) contain carbohy- 
drates, fats, and proteins; (14) are necessary for the germination of 
seeds ; (15) can be determined by simple tests. 

IV. The food supply of (16) seeds is found within the embryo of 
seeds having an endosperm ; (17) the corn seed is found in the cotyle- 
don; (18) the castor bean is stored in the endosperm; (19) dicoty- 
ledenous seeds is always stored in the endosperm ; (20) seeds is stored 
in the form of organic nutrients. 

V. Seeds, in order to use the food contained in them must (21) 
have it in a soluble condition ; (22) use it as a solid ; (23) digest it first ; 
(24) change it to such condition as will get into the cells; (25) be 
exposed to a high temperature. 

Achievement Test 

1. How do you make the tests for the different nutrients found in 
food? 

2. What ar£ all the experiments on germination? What factors 
are necessary to insure germination of seeds ? 

3. How can you prove that living things burn or oxidize food in 
order to release energy ? 

4. How can you make tests to prove that all living things have to 
digest food before they can use it? 

Practical Problems 

1. Prove what organic nutrients are present in a pea, a grain of 
corn, a lima bean, and a sunflower seed. Tabulate your results. 

2. Prove that some seed other than corn digests its food supply 
before using it for growth. 



REFERENCES 133 

3. What conditions outside a seed are necessary to make it grow? 
What conditions inside the seed ? 

4. Compare an engine with a plant or an animal. In what ways 
are they alike? 

5. Make diagrams to show how corn grains and bean seeds differ? 

6. How could you determine whether light is necessary for the germi- 
nation of seeds ? 



Useful Refekences 

Burlingame and others, General Biology. Chapter IV. (Henry Holt 

& Co. 1922.) 
Coulter, Barnes, and Cowles, Textbook of Botany, Vol. Two. (Ameri- 
can Book Company.) 
Eikenberry and Waldron, Educational Biology. (Ginn and Co. 1930.) 
Ganong, The Teaching Botanist. (The Macmillan Co.) 
Holman and Robbins, Textbook of General Botany, pp. 285-308. (John 

Wiley & Sons. 1928.) 
Hunter, New Laboratory Problems in Civic Biology. Unit VI. (Ameri- 
can Book Company.) 
Moore and Halligan, Plant Production. (American Book Company.) 
Trauseau, General Botany. Chapter VI. (World Book Co. 1923.) 
Waters, Essentials of the New Agriculture. (Ginn & Co. 1924.) 



H. BIO — 10 




SURVEY QUESTIONS 

How can roots take substances from the soil? Why do farmers use 
fertilizers ? Is it true that green plants are the largest food manufactories 
in the world. What do we mean by " corn on hoof " ? Why do we plant 
trees in city parks ? What value might green plants be in your home ? 



Photo by Wright Pierce 



UNIT VI 



GREEN PLANTS AS FOOD MAKERS AND FOOD 

USERS 

Preview. All of you will agree with the statement that food is 
probably the most important material in the world. There would 
be little chance for life on the earth if our food supply was taken 
away and we had no way of getting a new one. This is exactly 
what would happen if green plants would disappear from the 
earth. If you think it out, you can easily prove that all animals 
are dependent on green plants for food. For example, cows eat 
grass, and in turn, give man milk and meat. Plants may furnish 
man with food directly as vegetables, cereals, and fruits. Even 
the walrus and seal in the arctic regions, which at first sight would 

134 



PREVIEW 135 

seemingly be deprived of all plant food, yet live on fish which in 
turn exist almost entirely on sea weeds and small microscopic plants. 
Invariably we start with green plants which furnish food for animals. 

The green leaves of plants are really solar engines which get 
power from the sun and which manufacture foods only when the 
sun gives them this power. In order to make food the plant must 
have certain raw material on which to work : carbon dioxide from 
the air, and water and mineral salts from the soil. Another sub- 
stance must be present in the leaves, a green coloring matter 
called chlorophyll. This substance seems to be able to use the 
radiant energy of the sun better than any other living material. 

But since the raw material, out of which foods are made, is in 
the soil, the air, and the water which the plant receives, it is 
evident that we must account for some way of getting these various 
substances into the leaf. If one of the seedlings of a bean is 
placed in sawdust and is given light, air, and distilled water, it 
will die after the food in the cotyledons is used up. Soil is part 
of its natural environment and the roots which come in contact 
with the soil are very important structures. Not only does soil 
hold water, but this water contains certain dissolved mineral 
salts which are absolutely necessary for the life of the plant. 
Distilled water does not contain these mineral salts which come 
from the soil, consequently the plant will die. You have all read 
of how plants can be kept alive by feeding them " plant pills." 
These " plant pills " contain the necessary mineral salts which, 
when dissolved in water, are absorbed through the roots into the 
plant. These salts form a very important part of the living matter 
of which both plants and animals are composed. Hence the 
plant cannot grow without a small quantity of these materials. 

One of our big problems is to discover just how these dissolved 
mineral substances are taken in by the roots. We say roots 
absorb them, but how? A good scientist is not content with a 
statement ; he wants proof. To obtain this proof he must use a 
microscope and then he will see that the lower part of the small 
roots are covered with tiny outgrowths from the living cells of 
the root which immensely increase the absorbing surface of the 
roots. These little projections, called root hairs, are the organs by 



136 



GREEN PLANTS AS FOOD MAKERS 



means of which soil water, with the dissolved mineral materials, 
are taken into the root. But again we are met with a problem. 
Food is manufactured in the leaves of the plant, but all parts of 
the plant need that food. It is common knowledge that food is 
stored in seeds, in fruit, in stems such as the asparagus and in the 
roots such as turnips, radishes, and carrots. How then does the 
food get from the leaves to the various parts of the plant, and how 
does the water get from the roots to the leaves themselves where 




Wright Pierce 



In the growth of the bean plant, notice the gradual decrease in size and final disappear- 
ance of the cotyledons. How does the plant obtain food for growth after the cotyledons 
have been used? 



it is used in the manufacture of foods ? Here again we must call 
the microscope into play. You are all familiar with the fact 
that a celery stem is made up of a watery material with long, 
threadlike fibers in it. If we were to examine one of these thread- 
like structures under the microscope, we should find that it was 
made up of a large number of little tubes of various diameters, 
some large and some small. The larger tubes carry water, some 
of the smaller ones, food substances. We shall later find that these 
bundles of tubes, called fihrovascular bundles, are arranged in a 



COMPOSITION OF SOIL 137 

definite way in the stem ; that through these, in the inner bark of a 
woody stem, food passes down from the leaves, while in the woody 
stem inside, soil water passes up to the leaves. 

Again you might ask the question, how do solid foods pass 
through such tiny tubes? Not in a solid state, but in the form 
of dissolved food substances. We shall find that these foods are 
actually digested or made soluble by means of certain peculiar 
substances called enzymes which are found in the cells in different 
parts of the plant. Some of these enzymes seem to have the 
ability to change solid foods into soluble form, while others change 
the soluble foods back into insoluble substances. In this way we 
have starches, proteins, and oils stored in different parts of the 
plant. It will be the purpose of this unit to explain to us these 
various processes so that we may really understand how the plant 
makes food, how it transports it, and how it stores its surplus 
which is used for the benefit of the animal world, including man 
himself. 

PROBLEM I. WHAT DO PLANTS TAKE FROM THE SOIL? 

Composition of soil. As any one knows, the soil is composed 
of different substances in different localities. Contrast the black 
soil of Minnesota or Illinois with the sandy soil of Maine or Cali- 
fornia, or the red clay of Virginia. If we examine a small mass 
of garden soil carefully, we find that it is composed of numerous 
particles of varying size and weight. Between these particles, 
if the soil is not caked and hard packed, we can find tiny spaces, 
which are formed and enlarged when the soil is tilled. They 
allow the air and water to penetrate into the ground. If we exam- 
ine some soil under the microscope, we find considerable water 
clinging to the particles, thus forming a delicate film around each 
one. 

Under the microscope, also, most soils are seen to contain par- 
ticles of different kinds. Some are tiny pieces of rock, like those 
still being formed where solid rock is exposed to the weather. 
Rain, cold, and ice, working alternately with heat, chip off pieces 
of rock. These pieces in time may be worn smaller by the action 
of winds, running water, and in some places by glaciers. These 



138 



GREEN PLANTS AS FOOD MAKERS 



processes of soil making are aided by oxidation. A glance at some 
crumbling stones will give you an example of this yellow oxide of 
iron (rust) with which they are covered. So by slow degrees the 
earth became covered with a coating of what we call inorganic soil. 
Later, generation after generation of tiny plants and animals which 
lived in the soil died, and their remains formed the first organic 
materials of the soil. 

We shall later learn more about the bacteria or germs that live 
in the soil (see Unit VII, Problem III). It is sufficient at this 







i WbLi 



Note the slopes that are gradually being worn down and are forming soil in this canyon, 
desert soil is formed in this way. 



Much 



time for us to know that due to certain bacteria, dead plants and 
animals are changed through decay into matter which can be used 
by living plants. Living things must have nitrogen in order to 
make living matter. This nitrogen comes partly from the de- 
cayed material already in the soil, partly from fertilizers added by 
man, and partly from fresh nitrogen supplies taken from the air 
and " fixed " in a usable form by certain bacteria which live in the 
roots of leguminous plants like the bean or clover. 



WATER IN SOIL 



139 



Practical Exercise 1. Read some good reference book and report on how 
soil is formed. 

You are all familiar with the difference between so-called rich 
soil and poor soil. The dark soil contains more dead plant and 
animal matter, which forms the portion called humus. 

Humus contains organic matter. It is easy to prove that 
black soil contains organic matter, for if equal weights of carefully 
dried humus and of soil from a sandy road are heated red-hot for 
some time and then reweighed, the humus will be found to have 
lost considerably in weight, and the sandy soil to have lost very 
little. The material left after heating is inorganic material, 
the organic matter having been burned out. 

Demonstration 1. To find out if all kinds of soil hold the same 
amounts of water. 

Fill funnels of equal size with equal volumes of gravel, sand, barren 
soil, rich loam, leaf mold, and pulverized leaves — all dry — then 
pour equal amounts of water on them and measure all that runs 
through. Which soil holds the most water? 




Soil water a solution of mineral salts. Water, as it passes 
through the soil, gradually dissolves very minute portions of the 
chemical compounds of which the soil is composed, so that soil 
water is really a dilute solution of mineral salts. 

A plant needs mineral matter to make living matter. Living 
matter (protoplasm), besides containing the chemical elements 
carbon, hydrogen, oxygen, and nitrogen, contains very minute 
proportions of other elements which make up the basis of certain 



140 GREEN PLANTS AS FOOD MAKERS 

minerals. These are calcium, sulphur, iron, potassium, magne- 
sium, phosphorus, sodium, and chlorine. 

That plants will not grow well without certain of these mineral 
substances can be proved by the growth of seedlings in a so-called 
nutrient solution. If certain ingredients are left out of this solu- 
tion, the plants placed in it will not develop into adult plants. 

Practical Exercise 2. Make a table in which you indicate the relative 
amount of water that can be held by different kinds of soils. 

What kind of soil would you expect to find in a desert ? Covering the forest 
floor? In a river valley? 

Self-Testing Exercise 

Humus or (1) containing (2) (3) will 

hold (4) much better than inorganic soil. When water 

passes through the (5), it takes out certain mineral salts 

which it holds in (6). Such water is called (7) 

water. 

PROBLEM II. WHAT FACTORS INFLUENCE THE GROWTH 

OF ROOTS? 

Root system. Examine the root of a bean seedling grown in 
sawdust. The long main root is called the primary root. Other 
smaller roots which grow from the primary root are called secondary, 
and the roots growing from the latter are called tertiary roots or 
rootlets. What functions do these roots appear to have? Most 
of the roots examined take a more or less downward direction. 
Does gravity act on the growing root? This question may be 
answered by a simple experiment. 

Demonstration 2. To show the effect of gravity on a growing root. 

Plant mustard or radish seeds in a pocket garden. A very convenient 
form of pocket germinator may be made in a few minutes in the following 
manner : Obtain two cleaned four by five negatives (window glass will 
do) ; place one flat on the table and on it place half a dozen pieces of 
colored blotting paper cut slightly smaller than the glass. Now cut four 
thin strips of wood so as to fit on the glass just outside of the paper. 
Next moisten the blotter, place on it some well-soaked radish or mustard 
seeds or grains of barley, and cover it with the other glass. The whole 
box thus made should be bound together with bicycle tape. Seeds will 
germinate in this box, and with care may live for two weeks or more. 



ROOTS 



141 



Place the pocket garden on one edge, and allow the seeds to germinate 
until the root has grown to a length of about half an inch. Then turn it 
at right angles to the first position and allow it to remain for one day 
undisturbed. Turn it again. In a day or so examine it. Describe your 
results. 

The part of the root near the growing point is the one most 
sensitive to the change. This experiment indicates that the roots 
are influenced to 
grow downward by 
the force of gravity 
and that the grow- 
ing point is most 
responsive to this 
stimulus. 



primary 
secondary- 




Demonstration 3. 
Does water affect 
the course taken by 
roots ? 

Divide the in- 
terior of a shallow 
wooden box with 
glass side into two 
parts by a partition 
with an opening in 
it. Fill the box with 
sawdust. Plant peas 
and beans in the 
sawdust on one side 
of the partition, and 
water them very 
slightly, but keep the 
other side of the box 
well soaked. After 
two weeks, take up 
some of the seed- 
lings and note the 
position of the roots. 

Water a factor which determines the course taken by roots. 

Water, as well as the force of gravity, has much to do with the 
direction taken by roots. If radish seeds germinate on the under 
side of a moist sponge suspended in the air, their roots will turn 
against gravity and cling to the wet surface of the sponge. Water 
is always found below the surface of the ground, but sometimes 




taproot system fibro«*-ro«t, 

sveet clover- system of-vheat 

What is the length of the root system as compared with the height 
of the adult plant in each case ? 









A pocket garden. 



Wright Pierce 



Can you explain why the roots have taken the various positions indicated 
in the illustrations ? 

142 



STRUCTURE OF A ROOT 143 

at a great depth. Most trees and all grasses have a greater area 
of surface exposed by the roots than by the branches. The roots 
of alfalfa and sugar beets, in our Western States, often penetrate 
the soil for a distance of ten to twenty feet below the surface, until 
they reach that part of the soil which is always moist with under- 
ground water. 

Self-Testing Exercise 

A root system consists of ....;.. . (1), (2), and (3) 

roots. The end of the root is (4) to (5) and turns 

toward the center of the (6). Roots also respond to 

(7) in their environment and will penetrate many (8) 

into the (9) in order to get it. The effect of (10) 

on roots is seen by planting seeds in a (11) garden. 

PROBLEM III. HOW DOES THE STRUCTURE OF A ROOT 
FIT IT FOR ITS WORK? 

Demonstration 4. The finer structure of a root. Use a prepared 
slide or hand sections of bean roots stained with eosin or iodine and 
place it under a microscope. 

How a root is built. If we study the diagram on page 144 and 
compare it with what we see under the microscope, we find the root 1 
is made up of cells, the walls of which are rather thin. Over the 
lower end of the root is a collection of cells, most of which are dead, 
arranged loosely so as to form a cap over the growing tip. This is 
evidently an adaptation which protects the young and actively grow- 
ing cells just under the root cap. In the body of the root a central 
cylinder of wood can easily be distinguished from the surrounding 
cortex. It is in the cortex of fleshy roots that foods are stored, as 
in. the carrot or turnip. In a longitudinal section a series of tube- 
like structures may be found within the central cylinder. These 
structures are made up of cells which have grown together end to 
end, the long axis of the cells running the length of the main root. 
In their development these cells have grown together in such a 
manner as to lose their small connecting ends, and now form con- 
tinuous hollow tubes with rather strong walls. Other cells have 

1 Sections of tradescantia roots are excellent for demonstration of these 
structures. 



144 



GREEN PLANTS AS POOD MAKERS 



developed greatly thickened walls, which give mechanical support 
to the tubelike cells. Collections of such tubes and supporting 
woody cells together make up what are known as fibrovascular 

bundles in the wood. By this 



Central Cylinder- 
i§s£\._>*6oc{y bundle 




-root "hour 



epicCermis 



..root 



cctp 



system of tubes water is sent 
quickly from the roots to all 
parts of the plant body, pre- 
venting withering of leaves, 
and enabling the leaf to use 
water in food manufacture. 

Practical Exercise 3. What would 
you say was the use to the plant of 
a carrot root? Of the aerial roots 
of an ivy plant ? 

How would you go to work to 
find out what food substances are 
stored in a turnip or radish root? 
Of what value would these sub- 
stances be to the plant ? 

Laboratory Exercise. What 
are root hairs and where are 
they found ? 

Grow radish or mustard seeds 

;;|||lpl on blue blotting paper in Syra- 

"%S'-' J - cuse wa ^ch glasses, covering 

v '^Zr^ each watch glass with a thin 

A root, highly magnified. Find and give the glass plate. Describe the strUC- 
functions of the root cap, the woody bundles, and tures you see growing from the 

theroothairs - roots. These are called root 

hairs. Where are they the longest? Where the most abundant? 

Place root hairs of radish or mustard on a glass slide. Mount in a 
drop of water and cover with a cover slip. Examine with the low 
power of a microscope. What can you say of the thickness of their 
walls? Of how many cells does a root hair consist? If the root were 
covered with these thin-walled, delicate structures, what effect would 
they have upon the amount of absorbing surface of the root? 

Root hairs. Root hairs vaiy in length according to their position 
on the root, the longest root hairs being found some distance back 
from the tip. They are outgrowths of the outer layer of the root, 
the epidermis, and are of very great importance to the living plant. 

A single root hair examined under a compound microscope 
will be found to be a long, threadlike structure, almost color- 
less in appearance. The cell wall, which is very flexible and thin, 



ROOT HAIRS 



145 



is made up of cellulose. Clinging close to the cell wall is the pro- 
toplasm of the cell, the outer border forming a very delicate 
membrane. The interior of the 
root hair contains many vacuoles, 
or spaces, filled with a fluid called 
cell sap. Forming a part of the 
living protoplasm of the root hair, 
sometimes in the hairlike prolonga- 
tion and sometimes in that part 
of the cell which forms the epi- 
dermis, is found a nucleus. The 
nucleus, the membrane, and the rest 
of the protoplasm are alive ; the cell 
wall, formed by the living matter in 
the cell, is dead. The root hair is 
part of a living plant cell with a 
membrane and wall so delicate that 
water and dissolved mineral substan- 
ces from the soil can pass through them into the interior of the root. 
Functions of the root hairs. If a root containing a fringe of 
root hairs is washed carefully, it will be found to have tiny 
particles of soil still clinging to it. Examined under the micro- 
scope, these particles of soil seem to be cemented to the sticky 




.vacuole 

^ p ro toplasm. 

#^- beginning 
of ct rootTiafr* 

L.eell wall 



^..vacuole 

nucleus, 



a root hair 



The growth of a root hair. What are 
root hairs, according to this diagram? 




,-N/ater ..vacuole r tytoplasm- 
; -a'\r- rSoil ! -nucleus 






zmom 



u 



U^Xf^< 




plumule 



root hairs 



A corn root covered with root 
hairs which go between the 
particles of soil to get water 
and dissolved mineral matter. 



146 



GREEN PLANTS AS FOOD MAKERS 



surface of the root hair. The soil contains, besides chemical com- 
pounds of various mineral substances, — lime, potash, iron, silica, 
and many others, — much organic material. Acids of various kinds 
are present in the soil. They dissolve certain mineral substances 
in the water which is absorbed by the root hairs. Root hairs also 
give off small amounts of acid, which assist in dissolving minerals. 




• tf ops 

dilutee 
cccict = 




water 
audi 

phenolph 

and 

enoirgh 

base 

to turn 

pink 



A solution of phenolphthalein will lose its color if an acid is added to it. Explain why the 
solution of phenolphthalein (on the right) is losing its color. 

We say that the delicate root hairs absorb water, and since 
absorption is a process common to both plants and animal cells 
we shall study this phenomenon carefully in the next problem. 




Self-Testing Exercise 

A root is made up of (1). The outer layer, called the 

(2), is prolonged into many (3) walled structures 

called (4) (5). These take (6) and 

(7) (8) out of the soil. Root hairs give off a small 

amount of (9), which aids in (10) mineral salts. 



IMBIBITION 147 

PROBLEM IV. HOW DO ROOT HAIRS TAKE IN WATER 
AND SOIL SALTS? 

Demonstration 5. To show diffusion in gases and liquids. 

(a) Open a bottle of carbon bisulphide at one point in the school 
room. Show, by raising of hands, the time it takes for the odor of 
the gas to become noticeable in different parts of the room. (6) Place 
a little powdered eosin in a glass of water. Leave undisturbed for some 
hours. How long will it be before the entire glass of liquid is colored? 

Diffusion. We all know that certain substances, such as the 
odor of tobacco smoke or the perfumes of flowers, pass rapidly 
from the point where they are given off and tend to spread in all 
directions through the air. The odor of the orange blossoms in 
California is a memory to those who have driven near the orange 
groves. Substances which will dissolve in liquids will also diffuse 
through the liquids. In the diffusion of both gases and liquids 
particles of the substance pass from the place where they are most 
concentrated to where they are less concentrated, or lacking, the 
rate of travel being much slower in liquids than in gases. 

Imbibition. The passage of water from point to point by 
capillarity x does not account for soil water getting inside the cell. 
It has to go through the cellulose wall and the delicate membrane 
of protoplasm within. The walls of cells, like wood, absorb soil 
water readily by a process known as imbibition (mi-be-bish'wn) 
or absorption. This brings the soil water in contact with the cell 
membrane. Inside the cell membrane is a liquid which would 
diffuse freely with the soil water if the membrane were removed. 
But a membrane acts peculiarly toward diffusing substances. 

Osmosis. The process by which water with dissolved substances 
passes through the cell membrane is called osmosis. 

Demonstration 6. To show the process of osmosis. 

Carefully break away part of the shell of an egg so as to expose the 
delicate skin or membrane underneath. Thus we have a picture of 
the relation of the cell membrane (like the egg skin) to the cell wall 
(like the egg shell). Suspend this egg in a glass of cold water half an 
hour. What happens? 

If we test the water in the glass for protein, the organic sub- 
stance of which white of egg is composed, we shall find none. 

1 Capillarity (kap-i-lar'i-ti) : rise of liquids in a tube. 



148 



GREEN PLANTS AS POOD MAKERS 



Evidently the egg membrane will permit the passage of water 
but not of protein. Such a membrane is said to be semi-permeable 
(pur'me-d-b'l). It is this kind of membrane that surrounds plant 
and animal cells. It will permit certain substances such as water 
to pass through it readily in either direction, and it will permit 
certain substances in solution to pass less readily, while still other 
substances will not be permitted to pass through at all. 

Demonstration 7. Fill the lower end of a thistle tube with a solution 
of grape sugar and water. Tie tightly over it an animal membrane 
(as a pig's bladder or skin of frog's leg), and place the tube in water, 
as shown in the diagram. After a short time observe your apparatus. 
What has happened? Why? At the end of an hour, test the water in 
the beaker with Fehling's solution. Explain your result. 

If we could see the separate particles, or molecules, of the water 

and of the solution of water and sugar, they would be found to 

arrange themselves on each side of the membrane so as to cover 

it completely. But since the water mole- 

Icules pass easily through the membrane 
and the sugar molecules do not pass so 
easily, it will be seen that the inner side of 
the membrane does not present so much 
space for the diffusion of water particles as 
does the other side. Hence the flow of 
water into the tube is more rapid than the 
flow out of the tube, and the water gradually 
rises in the thistle tube. This passage of 
water through a semipermeable membrane 
is known as osmosis (os-mo'sis). It will be 
seen that the greater flow of water mole- 
cules is always from the point of greater 
concentration of water to the point of lesser 
concentration of water. If the solution is 
completely inclosed in a vessel with rigid 
walls, the entrance of more water will cause 
osmosis in an egg. Ex- a pressure by the solution within these 
plain, with reference to the c i ose d walls and will prevent the entrance 

text, why water will rise in r 

the tube. of any more water. This is known as 



.gkrss tube. 




■4-mernbrone 



ABSORPTION AND OSMOSIS 



149 




After reading the text, explain what has happened 
in the right-hand tube and beaker. 



osmotic pressure. But if the walls of the vessel are less rigid, as 
in the egg membrane, the osmotic pressure will cause the mem- 
brane to swell and distend until it eventually may burst. 

Why root hairs absorb water and soil salts. The wall of the 
root hair readily takes in water and dissolved soil salts by imbi- 
bition. The membrane sur- 
rounding the protoplasm of 
every living cell is a semi- 
permeable membrane, which, 
while allowing water and 
mineral salts in solution to 
pass or diffuse toward the in- 
side, will also allow some dif- 
fusion outward of the water 
and soluble materials within 
the cell. But the inward flow 
is much greater than the out- 
ward flow. As soon as the 
outer cells have increased their 

holdings of soil water, an osmosis inward from cell to cell is started 
because the water tends to flow from the place of its greater con- 
centration to the place of lesser concentration. Mineral salts in 
solution are carried along with the water so that the needed soil 
substances are carried along from cell to cell, until they reach the 
small tubes of the central cylinder. The osmotic pressure in the 
root hairs is sufficient to cause enough force in these tubes to raise 
a column of water to a considerable height in the stem. This is 
known as root pressure. 

Physiological importance of diffusion and osmosis. The 
processes of diffusion and osmosis are of great importance not 
only to a plant, but also to an animal. Foods are digested in the 
food tube of an animal ; that is, they are changed into a soluble 
form so that they may pass through the walls of the food tube and 
become part of the blood. The inner lining of part of the food 
tube (small intestines) is composed of millions of small fingerlike 
projections called villi, which look somewhat, in size at least, like 
root hairs. These villi are (unlike a root hair) made up of many 
h. bio — 11 



150 GREEN PLANTS AS FOOD MAKERS 

cells, through which liquid food passes into the blood. The 
process of absorption in animals is not entirely understood, but 
it takes place largely by diffusion and osmosis. Without these 
processes we would be unable to use most of the food we eat. 



Self-Testing Exercise 

In liquids and gases (1) of substances tend to pass from a 

place where they are more (2) to a place of less (3) 

by means of (4). If this takes place through a (5) 

(6), osmosis is said to take place. Substances in the 

(7) pass with the water through the (8) (9) 

into the (10) ....... .(11). 



PROBLEM V. WHAT OTHER PURPOSES DO ROOTS SERVE? 

Besides the purposes of anchorage and water absorption roots 
have other functions. They absorb oxygen as well as water from 
the soil into which they reach. The rows of dead trees around a 
pond that has been raised by damming indicates that one cause 
of the death of these trees was lack of oxygen. They were actually 
drowned. The so-called " cypress knees," projections of the roots 
from cypress trees, which grow in water, are adaptations to obtain 
oxygen, as they are not found on cypress trees living in dry 
localities. Food is stored in fleshy roots, like the carrot, turnip, 
or parsnip. Such stores of food enable the plants that produce 
seeds every other year (biennials) to get an early start the second 
year from this stored food. Some plants like the ivy produce roots 
on the stem, which help it in climbing. Such roots are called ad- 
ventitious. Another type of air roots is found in tropical plants, 
such as orchids. These have thickened roots with the special 
function of absorbing and holding water. Some plants, such as 
the strawberry, or couch grass, develop new plants by taking root 
wherever the reclining stem happens to touch the ground. Still 
another type of root is seen in the dodder, a parasitic plant. The 
root of this plant pushes its way into the stems of certain plants 
from which it absorbs its food. 



THE STRUCTURE OF A LEAF 

Practical Exercise 4. Fill out the following : 



151 



Types of Roots 


Functions 


Adaptations 


Examples 











Self-Testing Exercise 

Roots act as (1) and absorb (2) as well as 

(3) . Some roots store (4) . Plants may (5) by- 
means of (6). Many plants produce (7) wherever 

the (8) happens to (9) the ground (10) 

plants absorb food from the (11) on which they (12). 



PROBLEM VI. WHERE DOES THE GREEN PLANT 
MANUFACTURE FOOD? 

The primary function of the green leaf is the manufacture of 
food from the raw materials which are absorbed through the cell 
walls. 

Laboratory Exercise. Examine a leaf of maple or oak. Notice 
that it consists of two parts : a stem, the petiole, and a broad expanded 
part, the blade. Note, also, that the petiole leads into a number of 
branching veins which support the blade. Notice the arrangement 
of leaves. Can they all receive full sunlight? Estimate the amount 
of green leaf surface in a plant in the room by multiplying the surface 
area of one leaf by the number of leaves on the plant. Place in red ink 
the cut end of a growing shoot from a young tree or shrub. Leave for 
24 hours. What happens? 

State uses of the veins. Explain how the leaf is fitted to receive light. 

The structure of a leaf. In the experiment with the red ink 
and young shoots we shall find that the fluid has gone into the 
skeleton or framework of the leaf. Let us examine a simple leaf 
more Carefully. It shows usually (1) a flat, broad blade, which 
may take almost any conceivable shape ; (2) a stalk, or petiole, 
which spreads out into veins in the blade ; (3) stipules, a pair of 



152 



GREEN PLANTS AS FOOD MAKERS 



outgrowths from the petiole at its base. In many leaves the 
stipules fall off early. Some leaves are compound, that is, each of 





parallel 
veinect 



How do these leaves differ ? In what ways are they alike ? 

the little leaflike parts or leaflets is in reality a section of the leaf 
blade which is so deeply indented that it is cut away to the midrib 
or central vein, as in the rose leaf shown in the figure below. 

The cell structure of a leaf. The 
outer covering of a leaf, on both the 
upper and the lower surfaces, is 
called the epidermis, and is com- 
posed of large, irregular cells. The 
under surface of a leaf seen through 
a microscope usually shows many 
tiny oval openings, called stomata 
(sto'md-td, sing, sto'ma). Two cells, 
kidney-shaped, are found, one on 
each side of a stoma. These are the 
guard cells. By a change in the 
shape and size of these cells, due to 
absorption of water, the stoma is 
made larger or smaller. 
Study of the leaf in cross section 




f*stipules 



recc clover y rose 



How pan you tell that these are com- 
pound leaves? 



THE CELL STRUCTURE OF A LEAF 



153 




upper epidtermis of leaf 



shows that the stomata open directly into air chambers which pene- 
trate between and around the loosely arranged cells of spongy tis- 
sue composing the under part 
of the leaf. The position of the 
stomata varies in different kinds 
of leaves. Most have stomata 
only in the under epidermis, 
but some, as the water lily, 
have them in the upper epi- 
dermis only. Still others have 
them in both surfaces. The 
under surface of an oak leaf of 
ordinary size contains about 
2,000,000 stomata. Under the 
upper epidermis is a layer of 
green cells closely packed to- 
gether (called collectively the 
palisade layer) . These cells are 
more or less columnar in shape 
and have tiny green bodies in 
them. Air can easily pass 
through the stomata and be- 
tween the cells of the spongy 
tissue until it reaches the pali- 
sade layer. In a section of a leaf cut through a vein, we find 
the veins to be composed of a number of tubes made up of, and 

strengthened by, thick- 



walled cells. The veins 
are a continuation of 
the tubes of the stem 
which form the frame- 
work of the blade of the 
leaf. 

Practical Exercise 6. 

Study the opposite diagram 
carefully and draw one for 
your workbook that will show 
all the structures mentioned 




-Stoma. 



guard cell 

nucleus 

.chloropktst 



C. -vacuole 



lov/er epicCe^mis of leaf 

Compare the upper and lower surfaces of the leaf. 



epictermis 




tissue 



epidermis 



Stomal v duaroC Cell 

A cross section through a leaf, seen through the com- 
pound microscope. State the use of the vein, the stoma, 
the air spaces, the palisade layer, the epidermis. 



154 GREEN PLANTS AS FOOD MAKERS 

in the text. In this diagram make arrows to show (a) how air gets to the 
cells, (6) how water gets to the cells, and (c) how food materials made in the 
palisade layer might get out of the leaf. 

Self-Testing Exercise 

A green plant (1) food in its (2). The 

(3) is fitted for its work by being (4) and exposing a 

(5) surface to the (6). It contains many small openings 

called (7), through which (8) passes. The size of 

the (9) is controlled by (10) (11). A leaf 

is made up of a (12), (13), and (14). 



PROBLEM VH. WHAT RAW MATERIALS AND CONDITIONS 
ARE NEEDED TO MAKE FOOD? 

Demonstration 8. How does water get into leaves? 

Where is the passageway of water from the roots to the leaves? 
Place a young growing pea or bean seedling in red ink (eosin) and 
leave in the sun for a few hours. What happens? What happens 
after a wilted plant is given water ? Why ? Place celery stalks in red 
ink and leave for a few hours in the sunlight. Cut thin sections of the 
stem. Where does the colored water rise? It is obvious from these 
experiments that water rises through the minute tubes or ducts in the 
stems. We will find later in most woodj^ stems that these bundles of 
tubes are arranged in a very regular way. 

What raw materials are needed ? If we think back to our work 
on foods in the last unit, we may remember that organic foods 
consist of the elements carbon, oxygen, hydrogen, nitrogen, and 
small amounts of certain elements found in the soil, such as 
calcium, iron, potassium, and sodium. If the leaf is to manu- 
facture organic food substances, then we must see where these 
elements might come from. Water is made up of oxygen and 
hydrogen ; carbon dioxide, a gas given off in the breath, is in the 
air in small quantities, while nitrogen in a usable form is in soil 
that contains humus. Here then are the raw materials. How 
do they get into the leaf? 

We have just seen that water can get from the roots up through 
the stem and into the leaves. This water, if it comes from the soil, 
has dissolved in it mineral matter, including nitrates from which 
the plant may obtain nitrogen. Carbon dioxide, which is taken 



EFFECT OF LIGHT ON PLANTS 



155 



out of the air, is another of the raw materials. This gas enters the 
leaf through the stomata and thus comes in contact with the living 
cells of the leaf which are the manufacturers. 

Demonstration 9. To show the effect of light on green leaves. 

Place oxalis or nasturtium plants near a window. After several days, 
notice the position of the blades of the leaves. Notice also the leaf 
stalks. Account for the position of the leaves and stems. 

Effect of light on plants. Evidently sunlight has something to 
do with the life of a green plant ; for in young plants which have 
been grown in total darkness, no green color is found in either stems 
or leaves, the latter often 
being reduced to mere scales. 
The stems are long and more 
or less reclining, as those of 
a sprouting potato kept in 
darkness. We can explain 
the changed condition of the 
seedling grown in the dark 
only by assuming that lack 
of light has some effect on the 
protoplasm of the seedling 
and induces the growth of 
the stem. If seedlings have 
been growing on a window 
sill, or where the light comes 
in from one side, you have 
doubtless noticed that the 
stem grows towards the 
source of light and the leaves 
tend to arrange themselves 
so as to receive as much 
light as possible on their up- 
per surfaces. The illustra- 
tion here shows very plainly 
the effect of light on a grow- 
ing plant. A hole was cut in one end of a box and barriers were 
erected in the interior of the box so that the seeds planted in the 




Wright Pierce 
Explain why this plant has grown toward the right 
of the box instead of the left. 



156 



GREEN PLANTS AS FOOD MAKERS 



sawdust received their light by an indirect course. The young 
seedling in this case responded to the influence of the stimulus 
of light so that it grew out finally through the hole in the box into 
the open air. This growth of the stem to the light is of very 
great importance to a growing plant, because food making depends 
largely on the amount of sunlight the leaves receive. 

Practical Exercise 6. Why do the leaves of lettuce or cabbage when 
"headed" turn white? 

Effect of light on leaf arrangement. It is a matter of common 
knowledge that green leaves turn toward the light. Place growing 



1 


1^* 


4f 

1 



Brootclyn Botanical Garden, N. Y. 
Why are the leaves of these plants well arranged for obtaining sunlight ? Why do they need a 

great deal of sunlight ? 

pea seedlings, oxalis, or any other plants of rapid growth near 
a window which receives full sunlight. Within a short time the 
leaves will be found in positions to receive the most sunlight 
possible. Careful observation of any plants growing outdoors 
shows us that in almost every case the leaves are so arranged as 
to get much sunlight. The ivy climbing up a wall, the morning- 
glory, the dandelion, and the burdock, all show different arrange- 
ment of leaves, each presenting a large surface to the light. Leaves 
are often definitely arranged, each fitting in between others so as 
to present their upper surface to the sun. Such an arrangement 
is known as a leaf mosaic. Examples of such mosaics are seen on 
trees having leaves that come out from the branch alternately, first 



CARBOHYDRATE MAKING 157 

on one side and then on the other. In the horse-chestnut, where 
the leaves come out opposite each other, the older leaves of an up- 
right branch have longer petioles than the younger ones. In the 
case of the dandelion, a rosette or whorled cluster of leaves is found. 
Here the leaves are arranged spirally on a very short stem. Leaves 
with long petioles are nearest the ground while those with shorter 
petioles alternate with them, filling the space. In the mullein the 
entire plant forms a cone. The old leaves near the bottom are 
very large, and the younger ones near the apex are much smaller and 
come out close to the main stalk. In every case each leaf receives 
a large amount of light. 

Practical Exercise 7. Bring into class as many examples of various leaf 
arrangement as possible. 

The sun a source of energy. We have already learned that green 
plants are the great food makers for themselves and for animals. 
We are now ready to learn how green plants make food. We know 
the sun is the source of most of the energy that is received on this 
earth in the form of heat and light. Every one knows what 
" burning glass " will do when it focuses the sun's rays on a piece 
of paper. Solar engines have not come into any great use as yet, 
because fuel is cheaper, but some day we undoubtedly shall harness 
the energy of the sun to do our everyday work. Experiments have 
shown that as much as 80 per cent of the radiant energy falling on 
certain green leaves is absorbed. Part of this energy is used by 
the leaf; but part is changed to heat, raises the temperature of 
the leaf, and is later lost to the air if the air is cooler than the leaf. 
Regulation of this temperature is obtained in much the same way 
as in our own bodies, by evaporation of water. We perspire ; the 
leaf passes off water vapor, largely through the stomata. 

Relation of light and air to starch in leaf. We can readily test 
how light affects the amount of starch found in a leaf. We do this 
by pinning strips of black cloth, such as alpaca, over portions of 
several leaves of a growing hydrangea which has previously been 
placed in a dark room for a few hours, and then putting the plant 
in direct sunlight for an hour or two. We remove the partly cov- 
ered leaves, boil them to soften the tissues, and extract the chloro- 
phyll with wood alcohol (because the green color of the chlorophyll 



158 



GREEN PLANTS AS FOOD MAKERS 




H2O 2 
starch made 




warm alcohol 
extracts, 
green color' 




decolori^ecL 

Mi t 

iodine 




What effect does 
sunlight have on green 
leaves ? Describe the 
experiment which will 
prove this. 



interferes with the blue color of the starch test). 
A test with iodine shows that starch is present 
only in the portions of the leaves exposed to sun- 
light. From this we infer that the sun has some- 
thing to do with the amount of starch found in a leaf. 

The necessity of air for making carbohydrates 
may easily be proved by experiments. For if 
parts of several leaves on a plant are covered with 
vaseline, they will be found to contain no starch, 
while those parts of the leaf without vaseline, but 
exposed to the sun and air, will contain starch. 
The part of the air used in carbohydrate-making 
is carbon dioxide, which is present in the atmos- 
phere in very small amounts. 

Air is necessary for the process of making sugar 

and starch in a leaf, not only because carbon 

dioxide gas is absorbed but also because the leaf 

is alive and must have oxygen in order to do 

its work. It takes this oxygen from the air. 

Practical Exercise 8. Explain wiry some plants do so 
poorly in the house. Why are trees in cities often so 
sickly? 

Demonstration 10. To show the need of chloro- 
phyll for making carbohydrates. 

Place a plant with variegated leaves, as Coleus, in 
sunlight for an hour or two. Test several leaves with 
iodine after removing the chlorophyll with methyl 
alcohol. Do all the leaves show presence of starch? 
Do all parts of the variegated leaves show starch? 
Why is chlorophyll necessary? 

Demonstration 11. To show the need of carbon 
dioxide for making carbohydrates. 

Place a green plant in a wide-mouth jar which 
contains carbon dioxide gas. Place the jar in bright 
sunlight. Place another plant in a jar in which 
carbon dioxide is removed by means of soda lime 
(see diagram) . After 24 hours test leaves from both 
plants for starch. Results ? 

Chlorophyll necessary for making carbohy- 
drates. In the palisade layer of the leaf, we find 
cells which are almost cylindrical in form. In 



USE OF CHLOROPHYLL 



159 



the protoplasm of these cells are found a number of tiny green 
bodies, the chloroplasts or chlorophyll bodies. If the leaf is 
placed in wood alcohol, we find that the bodies still remain, but 
that the color is extracted, going into the alcohol and giving to 
it a beautiful green color. The chloroplasts are, indeed, simply 
part of the protoplasm of the cell colored green. These bodies 
are of the greatest importance directly to plants and indirectly to 
animals. The chloroplasts, by means of the energy received from 
the sun, manufacture 



air- 



airv 



sugars and then starch 
out of certain raw ma- 
terials obtained from the 
soil and the air. These 
raw materials are soil 
water, which is passed 
up from the roots through 
the bundles of tubes into 
the veins of the leaf, and 
carbon dioxide from the 
air, which is taken in 
through the stomata or 
pores. A plant with va- 
riegated leaves, as the 
tradescantia or " wander- 
ing Jew," makes starch 
only in the green part of the leaf, though these raw materials 
reach all parts of the leaf. 

Changes in color in leaves. Green leaves are really solar engines 
and like all machinery wear out after long usage. It has been 
estimated that the total working life of a green leaf is about 1500 
hours. In the fall we find leaves changing color, and we used to 
think this was due to the action of frost. Now we think it is due 
to the breaking down of the green coloring matter in the leaf. 
This disintegration seems to be an oxidation process. As the 
chlorophyll disappears from the leaves, the yellow color, which is 
present in the leaf cells, can now be seen. But other autumn 
colorations are not yet fully understood. 




Explain the difference in growth of the two plants. 



160 GREEN PLANTS AS FOOD MAKERS 

Practical Exercise 9. Make a collection of leaves showing as many color 
changes as possible. 

Self-Testing Exercise 

Water rises in the stem of plants through (1) (2). 

The green leaf needs (3), (4), and (5) 

(6) in order to manufacture organic food. These materials 

enter the plants through the (7) in the leaves and through 

the (8) in the soil. Plants growing in total darkness are 

without (9) (10) (11). This material is 

known as (12). 

PROBLEM VIII. WHAT ARE THE PRODUCTS AND RESULTS 
OF FOOD MANUFACTURE? 

Comparison of carbohydrate-making and milling. The manu- 
facture of carbohydrate by the green leaf is not easily understood. 
The process has been compared to the work of a mill. In this 
case the mill is the green part of the leaf. The sun furnishes the 
motive power, the chloroplasts constitute the machinery, and soil 
water and carbon dioxide are the raw products taken into the 
mill. The manufactured product is sugar which is later changed 
into starch. A certain by-product (corresponding to the waste 
in a mill) is also given out. This by-product is oxygen. To un- 
derstand the process better, we must refer to the diagram of the 
leaf (page 161). Here we find that the cells of the green layer 
of the leaf, under the upper epidermis, perform most of the work. 
The carbon dioxide is taken in through the stomata and reaches 
the green cells by way of the intercellular spaces and by diffusion 
from cell to cell. Water reaches the green cells through the veins. 
It then passes into the cells and there becomes part of the cell sap. 
The light of the sun easily penetrates the cells of the palisade layer, 
giving the energy needed to make the starch. This whole process 
is a very delicate one, and will take place only when external 
conditions are favorable. Chlorophyll absorbs light of certain 
wave lengths, the blue and red rays do most of the work in food 
manufacture. For example, too much heat or too little heat stops 
carbohydrate-making in the leaf. The leaf engine works rapidly 
under favorable conditions and makes sugar in such quantities that 



PROTEIN-MAKING 



161 



it clogs up the conducting tubes and slows up the process of 
food making. But at night the foods are changed into a soluble 
form, transported to other parts of the plant, and the leaf is ready 
to begin its wurk again with the shining of the sun. This building 



ligbt energy light energy 




food 

is 

carried 

special 
tubes 



vateris 
carried 
to leaf 

by ' 

tubes 
Connected 
vith roots 



oxygen 

isjcriverz 
N/hen 
poet is 
macte 



i 



^air enters* 
Txath 
carbon 
ctioxicte^ 

C0 2 



The leaf food factory. Where is the light energy used? How do the raw materials get to the 
factory ? Where do waste products go ? Where do the manufactured products go ? 



up of carbohydrates, with the release of oxygen by the chloroplasts 
in the presence of sunlight, is called photosynthesis. 

Manufacture of fats. Inasmuch as tiny droplets of oil (or fat) 
are found inside the chlorophyll bodies in the leaf, we believe that 
fats, too, are made there, probably by a transformation of the 
starch already manufactured. 

Protein-making and its relation to the making of living matter. 
Protein is a part of the food which is necessary to form protoplasm. 
It is present in the leaf and is found also in the stem and root. 



162 GREEN PLANTS AS FOOD MAKERS 

Proteins can be manufactured in any of the cells of green plants 
where starches or sugars and certain salts are found. The presence 
of light does not seem to be a necessary factor for the process. 
How they are manufactured is a matter of conjecture. The 
minerals, nitrates, sulphates, and phosphates in the soil water 
give nitrogen, sulphur, and phosphorus, and the sugar or starch 
gives carbon, hydrogen, and oxygen, all of which elements are 
found in proteins. Proteins are probably not made directly into 
protoplasm in the leaf, but are transported to other parts of the 
plant, stored there and used when needed, either to form new 
cells or to repair waste. 

Enzymes and their work. It is a matter of common knowledge 
that starch food is stored in fruits, seeds, roots, and stems. We 
also know that starches cannot pass from one part of the plant to 
another because they are insoluble substances. The particles of 
which they are formed cannot go through the membranes which 
surround each cell in the plant. To make possible the circulation 
of food from one part of the plant to another insoluble foods must 
be made soluble. This is done by means of substances called 
enzymes. We have little knowledge of their actual composition, 
but we do know that they have the power to speed up chemical 
action in the cells so as to cause certain insoluble substances to 
become soluble. Each nutrient requires a specific enzyme to 
change it from an insoluble to a soluble form. This process which 
seems to go on in almost all plant cells as well in the darkness as 
in the daylight, is called digestion. 

Functions of food. While plants and animals obtain their 
food in different ways, they probably make it into living sub- 
stance {assimilate it) in the same manner. Foods serve exactly 
the same purposes in plants and in animals ; they either are used 
to build living matter or they are burned (oxidized) to furnish 
energy (power to do work). If you doubt that a plant exerts 
energy, note how the roots of a tree bore their way through the 
hardest soil, and how stems or roots of trees often split hard rocks. 

Relation of carbohydrate-making to human welfare. Leaves 
which have been in darkness show starch to be present soon after 
exposure to light. A corn plant may send almost half an ounce 



EVAPORATION OF WATER 



163 



of reserve food into the ears in a single day. The formation of 
fruit and the growth of grain, potatoes, and other food crops 
show the economic importance of the work of green leaves. Not 
only do plants make their own food and store it away, but they 
make food for animals as well; and the food is stored in such a 
stable form that it can be kept and sent to all parts of the world. 
Animals, herbivprous and flesh-eating, man himself, all are depend- 
ent upon the starch-making processes of the green plant for the 
ultimate source of their food. When we consider that in 1928 in 
the United States the total value of all farm crops was about 
$12,000,000,000, and when we realize that these products came 
from the air and soil through the energy of the sun, we may under- 
stand why the study of plant biology is of great importance. 

Practical Exercise 10. Make a table in which you list all the food products 
obtained in your community from green plants. 

Water is given off from the leaf. Much more water is taken in 
by the plant than is used by the plant. This water is given off 
through the leaves. 

Demonstration 12. Take some well-watered potted green plant, as a 
geranium or hydrangea, cover the pot with sheet rubber, fastening the 



jar. 




Covered 
vith sheet 
rubber— 



stare 



24 hours later 



rubber close to the stem of the plant. Next weigh the plant with the 
pot. Then cover it with a tall bell jar and place the apparatus in the 
sun. In a short time drops of moisture are seen to gather on the inside 
of the jar. If after a few hours we weigh the potted plant again, we 
find it weighs less than before. Obviously the loss comes from the 
water vapor which has escaped from stem, or leaves, or both. 



164 GREEN PLANTS AS FOOD MAKERS 

Evaporation of water. During the day an enormous amount 
of water is taken up by the 'roots and passed out through the 
leaves in the form of vapor. So rapid is this evaporation, or 
transpiration, in a small grass plant, that the water evaporated 
in a day may weigh more than the plant. It is estimated that 
nearly half a ton of water may be given off into the air during 
twenty-four hours by a grass plot 25 by 100 feet, the size of 
the average city lot. It is estimated that a corn plant in the 
Central West gives off more than forty gallons of water during 
its lifetime. Nearly 20,000 lbs. of water is given off between 
June and November by a good-sized birch tree. Fields of 
wheat are said to give off an amount of water equal to nearly 
20 per cent of the total rainfall on their area. The amount 
of water lost by plants through evaporation is many times 
more than the amount that goes into making food and living 
matter. 

Factors in transpiration. The amount of water lost from a 
plant varies greatly under different conditions. The humidity 
of the air, its temperature, and the temperature of the plant all 
affect the rate of transpiration. The stomata also tend to close 
under some conditions, thus helping to prevent evaporation. 
Certain experiments indicate that the plant probably has some 
control over the stomata. The stomata are usually closed at 
night but remain open from shortly after sunrise until late in the 
afternoon. They begin to close in the middle of the afternoon, and 
thus decrease the amount of water lost in the latter part of the 
day. Plants droop or wilt on hot, dry days because they cannot 
obtain water rapidly enough from the soil to make up for the loss 
through the leaves. Hairs on the leaf surface, waterproofing of 
outer cells, a decrease in leaf area, close grouping of leaves, the 
absence of leaves, as in the cactus, and the turning of leaves 
edgewise to light are all modifications which help to hold water 
in the body of the plant. 

Green plants give off oxygen in sunlight. In still another way 
green plants are of direct use to animal life. During the process 
of sugar-making, oxygen is given off as a by-product. This may 
easily be proved by the following experiment. 



RESPIRATION BY LEAVES 



165 



s^\ 




Demonstration 13. Place any green water plant in a battery jar 
partly filled with water, 1 cover the plants with a glass funnel, and 
invert a test tube full of water over the mouth of the funnel. Place 
the apparatus in a warm sunny window. Bubbles of gas are seen to 
rise from the plant. After several hours in the direct sunlight, enough 
of the gas may be obtained by dis- 
placement of the water to prove, 
by the rapid oxidation of a glow- 
ing splinter of wood in the gas, 
that oxygen is present. 

That oxygen is given off as a 
by-product by green plants is a 
fact of far-reaching importance. 
The green covering of the earth 
gives to animals an element 
that they must have, while the 
animals in their turn supply 
to the plants carbon dioxide, 
a compound used in food mak- 
ing. Thus a widespread relation 
of mutual helpfulness exists be- 
tween plants and animals. 

Respiration by leaves. All living things require oxygen. It 
is by means of the oxidation of food materials within the plant's 
body that the energy used in growth and movement is released. 
k plant takes in air with its oxygen largely through the stomata 
of the leaves, to a less extent through the lenticels 2 in the stem, and 
through the roots. Thus rapidly growing tissues receive the 
oxygen necessary for them to perform their work. One of the 
products of oxidation in the form of carbon dioxide is also passed 
off through these same organs. It can be shown by experiment 
that a plant uses up oxygen in the darkness and gives off carbon 
dioxide; in the light the amount of oxygen given off as a by- 
product in the process of carbohydrate-making is much greater 
than the amount used by the plant in respiration. 

1 Water contains air in solution, including some carbon dioxide, but the amount 
may be too small. Immediate success with this experiment will be obtained only 
if the water has been previously charged with carbon dioxide. 

2 Lenticels (lSn'ti-sSls) : lens-shaped spots or warts on the surface of young 
stems and shoots of peach, apple, and other trees. 

H. BIO — 12 



."v/ater-aud 

car-bon 
diovicCe, 



green plant. 



Explain just what is happening here and the 
conditions necessary to bring it about. 



166 GREEN PLANTS AS FOOD MAKERS 

Practical Exercise 11. Fill out the following table on the work of the leaf. 



Pabt 


Function 


What Happens 


What Causes It to Happen 











Self-Testing Exercise 

Green plants manufacture (1), (2), and 

(3). The manufacture of (4) by green plants in the presence 

of sunlight is called (5) . (6) is not a necessary 

factor for protein-making. In order for food to circulate from one 

part of the plant to another, the (7) food must be made 

(8). This change is caused by (9), and is known as 

(10). Food is needed for (11) and (12). 

Green plants give off (13) (14), (15) t and 

(16). 

PROBLEM IX. HOW IS FOOD CIRCULATED IN A PLANT? 

The circulation and final uses of food in green plants. We 

have seen that cells of green plants make food — especially the 
cells that are in the leaves. But all parts of the bodies of plants 
grow. Roots, stems, leaves, flowers, and fruits grow. Seeds 
are storehouses of food. We must now examine the stem of some 
plant in order to see how food is distributed, stored, and finally 
used in the various parts of the plant. 

The structure and growth of a dicotyledonous or woody stem 
If we cut a cross section through a young willow or apple stem, we 
find it shows three distinct regions. The center is occupied by 
the spongy, soft pith; surrounding this is found the rather tough 
wood, while the outermost area is bark. More careful study of the 
bark reveals the presence of three layers — an outer layer, epidermis, 
a middle green layer, cortex, and an inner fibrous layer. The inner 
layer is made up largely of tough fiberlike cells known as bast fibers. 



DICOTYLEDONOUS STEM 



167 



The most important parts of this inner bark, so far as the plant 
is concerned, are many tubelike structures known as sieve tubes. 



.-bark- 




.Cambium 
layer" 



. annual 
'"rings 



pith 
Toys 



Explain growth in this stem. 



These are long rows of living cells, having perforated sievelike 
ends. Through these cells food materials pass downward from 
the upper part of the plant, where they are manufactured. 

In the wood will be noticed a number of lines called medullary 
rays, or pith rays, radiating outward from the pith toward the 
bark. These are thin plates of pith which separate the wood into 
a number of wedge-shaped masses. The masses of wood contain 
many elongated cells, which, placed end to end, form thousands of 
little tubes connecting the leaves with the roots. In addition to 
these are many thick-walled cells, 

which give strength to the mass of y***^ -^^^^ 

wood. The bundles of tubes with / —-S^ortex 

their surrounding hard-walled cells / ^^^W^^VJcJmbium 
are the continuation of the bundles / 
of tubes which are found in the I (p> pith 
root. In sections of wood which 
have taken several years to grow, 
we find so-called annual rings. The 
distance between one ring and the 
next (see diagram) usually repre- 
sents the amount Of growth in One Cross section of a very young dicoty- 
r\ ±1- j. i i £ ledonous stem, showing arrangement and 

year. (jrrOWtn takes place trom a parts of the bundles and the other tissues. 




168 



GREEN PLANTS AS FOOD MAKERS 



layer of actively dividing cells, known as the cambium layer. This 
layer forms wood cells from its inner surface and bark from its 
outer surface. Thus new wood is formed as a distinct ring around 
the old outer wood and new bark inside the old bark. 

In a very young dicotyledonous stem before the wood of the 
bundles has formed an annual ring, these individual fibro-vascular 
bundles are quife separate, arranged in a circle around the cen- 
tral pith. Each bundle consists of three parts : the outer part, 
pJdeom, made up of the bast fibers and sieve tubes, through 
which liquids pass downwards: the middle part, cambium, or 

growth portion which soon 
develops also between the 
bundles and thus forms the 
cambium layer: and an 
inner part, xylem, made up 
of woody fibers and ducts 
with woody walls through 
which liquids pass upward 
through the stem. 

Use of the outer bark. 
The outer bark of a tree is 
protective. The cells are 
dead, but the heavy woody 
skeletons prevent the 
evaporation of fluids from 
within. The bark also 
protects the tree from 
attacks of plants or animals 
which might harm it . Most 
trees are provided with a 
layer of corklike cells. This 
layer in the cork oak is 
thick enough to be of com- 
mercial importance. There 
are many lenticels scattered 
These can be seen easily in a 




In this experiment the willow twig was girdled by 
taking off the bark. Can food now reach the part be- 
low the ring ? Why have roots come out aDove the 
ring? Why has a sprout appeared below the ring? 



through the surface of the bark 

young stem of apple, beech, or horse-chestnut. 



MONOCOTYLEDONOUS STEM 



169 



Demonstration 14. To show that food passes downward in the 
bark. If a freshly cut willow twig is placed in water, roots develop 



under water. If the stem then 




from that part of the stem which i 
is girdled by removing the bark 
in a ring just above where the 
roots are growing, the latter will 
eventually die, and new roots 
will appear above the girdled 
area. The passage of food ma- 
terials takes place in a downward 
direction outside the wood in the 
layer of bark which contains the 
bast fibers and sieve tubes. 

This experiment with the twig 
explains why trees die when 
girdled so as to cut the sieve 
tubes of the inner bark. Many 
of the birches of our forests 
have been killed, as a result of 
being girdled by thoughtless 
visitors. In the same way gnaw- 
ing animals frequently kill fruit 
trees. To a small extent food 
substances are conducted in the 
wood itself, and food passes 
from the inner bark to the cen- A cornstalk WLat are the differences in the 

ter Of the tree byway Of the pith arrangement of the fibrovascular bundles here 

and in a dicotyledonous or vascular stem ? 

rays m which starch is stored. 

Structure and growth of a monocotyledonous stem. A piece of 
cornstalk is made up of pith, through which are scattered numer- 
ous stringy, tough structures called fibrovascular bundles. The 
latter are the woody bundles of tubes and fibers which pass 
through the pith and run into the leaves, where (in young speci- 
mens) they may be followed as veins. The outside of the corn 
stem is formed of large numbers of fibrovascular bundles, which, 
closely packed together, form a hard, tough outer rind. Thus the 
woody material on the outside gives mechanical support to an 
otherwise spongy stem. In a very young stem epidermis is present. 

In the monocotyledonous stem the bundles are scattered and 
the cambium layer is absent. The bundles increase in number as 



fibrovascular 
DuncLle, 



170 



GREEN PLANTS AS FOOD MAKERS 



the stem grows older. Sieve tubes or phloem are in the outer part 

and xylem or water-bearing tubes in the inner part of the bundle. 

What causes water to rise in a stem. We have already seen that 

osmosis is responsible for getting water inside the root, and that 

the pressure exerted by this 
water (root pressure) is fre- 
quently capable of forcing 
fluids a considerable dis- 
tance up a living stem 
sometimes 20 or 30 feet in 
height. But during most 
of the year root pressure 
plays a very unimportant 
part in this phenomenon. 
It has been found that in 
the very tiny tubes, such 
as we find in wood, the 
rising column of water is 
held together by the force 
of cohesion. A core of 
water in tubes ^ °f an 




"feoct, __ 
distributed 
bv tubes 
to needV 
plant parts- 



soil sv&ter 

Yiasa part 

mthe 

waking €f 
foocC 1T1 
the leaf 



soil Vater- 
travels 

tubefto 
leaves 



, Soil 

W*-vater 

^ enters 

''^ plants 

- - through 

rootr 

Yiacirs- 



inch in diameter will with- 
stand a pull of over 4600 
pounds to the square inch, 
so it is likely that this force 
is the strongest factor in 
raising water in the tubes 
of tall trees. Also a very 
large amount of water is 
evaporated every day, a 

Fluids pass up and down in plants through tubes, tree of average size Using 
Raw materials pass upward into the leaves. The & & 

food manufactured in the leaves passes downward from 75 to 100 gallons of 
to the roots for storage, and to the other parts of the , ., r ,. i 

plant which need it. water daily, most of which 

passes out through the 
stomata. This evaporation may cause a pull on the volume of 
water in the fibrovascular bundles and probably is another im- 
portant factor in the rise of fluids in stems. 



DIGESTION AND STORAGE OF FOOD 171 

Digestion and storage of food. Much of the food made in the 
leaves is stored in the form of starch. But starch, being insoluble, 
cannot be passed from cell to cell in a plant. In our study of the 
root hair we found that substances in solution (solutes) will pass 
from cell to cell by osmosis. In our study of a growing seedling 
we found that a solid food substance, starch, was digested in the 
corn grain by an enzyme, thus becoming a diffusible substance which 
could pass from cell to cell. This process of digestion seemingly 
may take place in all living cells of the plant, although most of it 
is done in the leaves. In the bodies of all animals, including man, 
starchy foods are changed in a similar manner, but by other 
enzymes, into soluble grape sugar. 

The food material may be passed along in a soluble form until 
it comes to a place where food storage is to take place, and then 
it can be transformed again by the action of a reversible enzyme 
into an insoluble form (starch, for example) ; later, when needed 
by the plant in growth, it may again be transformed and sent in a 
soluble form through the stem to the place where it will be used. 

In a similar manner, protein seems to be changed and trans- 
ferred to various parts of the plant. Some forms of protein are 
soluble and others insoluble in water. White of egg, for example, 
is slightly soluble, but can be rendered insoluble by heating it so 
that it coagulates. Insoluble proteins are digested within the 
plant ; how and where is but slightly understood. Soluble pro- 
teins pass down the sieve tubes in the bast and then may be stored 
in the bast or medullary rays of the wood in an insoluble form, 
or they may pass into the root, fruit, or seeds of a plant, and be 
stored there. This stored food becomes of immense value to 
mankind, for it forms not only our cereal, potato, and other 
crops, but also our fruits of all kinds. 

Self-Testing Exeecise 

The center of a dicotyledonous stem is the (1). The outer 

area of bark of a tree gives (2) to the tree. The inner layer 

is made up of (3) '.(4). It contains the (5) 

(6) through which food materials pass downward to the roots. 

Growth takes place in the . (7) forming new (8) and 



172 GREEN PLANTS AS FOOD MAKERS 

a new inner layer of (9). The breathing holes on the sur- 
face of bark are called (10). The main bulk of a monocoty- 

ledonous stem is made up of (11), through which (12) 

(13) are scattered. The rise of water in a stem is brought 

about by the (14) of water from the tree and by the 

(15) of (16). Foods are (17) and are 

transported to all parts of the (18). 




cork 

outer corteK 
vascular 

--pith. 

-bud. 



PROBLEM X. WHY ARE PLANTS MODIFIED? 

Modified stems. We have already seen that the factors of the 
environment, light, heat, gravity, moisture, air currents, and other 

factors act upon the living 
substance of plants, caus- 
ing them to react in vari- 
ous ways. The changes 
which take place usually 
fit the plant to succeed 
better in its battle for life. 
Thus various modifications 
of stems have been brought 
about. The potato tuber 
is simply a much thickened 
storage stem. The tiny 
projection growing within 
the eye is a bud, which 
may give rise to a branch 
later. Some stems have 
come to exist underground 
because of the protection 
thus afforded. The pest 
called couch grass or quick 
grass has such a stem. 
Bulbs, like the onion or 
lily, are examples of stems which have become shortened and 
covered with thickened leaves, filled with food. Still other stems, 
like that of the dandelion, have become reduced in length, which 
prevents them from being broken off by grazing animals. 




scaler 



-/-terminal KtcC 
lateral "bucC 



Cross sections of a potato and of an onion. How 
can you show that these are modified stems? 



TESTS 173 

Climbing stems, as a result of the stimulation of the sun, twist 
around a support in a given direction, sometimes revolving with 
and sometimes against the course of the sun. 

We also find stems and leaves modified to become holdfasts as 
the tendrils found in climbing plants. Thorns, a protection from 
animals, may be modified parts of leaves or of stems. 

Practical Exercise 12. Make a list of the modified stems found in your 
locality. Show how each modification may be of use to the plant. 

Self-Testing Exekcise 

A modified stem is one that has probably been changed by the 

(1) in the (2) . Modified stems may be in the form 

of (3) as in the (4) . Some stems may be (5), 

while others may be (6), forming (7) . 

Review Summary 

Test your knowledge of the unit by (1) rechecking the survey questions; 

(2) performing all assigned exercises ; (3) checking with your teacher all tests 
and making up all missed parts ; (4) making an outline of the unit for your 
notebook. 

Test on Fundamental Concepts 

In a vertical column under the heading correct write numbers of all statements you believe 
are true. In another column under incorrect write numbers of untrue statements. Your 
grade = number of right answers X 2. 

I. Roots (1) grow toward water; (2) are affected by gravity; 

(3) may take carbon dioxide from the soil; (4) always store food; 
(5) hold a plant firmly in the ground. 

II. A root is able to take in water (6) because it is made of woody 
tissue ; (7) by means of osmosis ; (8) because it has a root cap covering 
each tiny root ; (9) through minute root hairs ; (10) because it gives 
off an acid. 

III. Roots are useful to plants because they (11) may store food; 
(12) gtow against gravity; (13) absorb mineral matter from the soil; 
(14) act as anchors ; (15) take in oxygen through their stomata. 

IV. The process by which food is made by green leaves is known as 

(16) transpiration; (17) protein-making; (18) nutrition; (19) photo- 
synthesis ; (20) osmosis. 



174 GREEN PLANTS AS FOOD MAKERS 

V. Green plants breathe through (21) lenticels; (22) root hairs; 
(23) stomata; (24) guard cells; (25) epidermal cells. 

VI. Food in plants is made soluble by (26) water ; (27) enzymes ; 
(28) the palisade layer of cells ; (29) oxygen ; (30) digestion. 

VII. A green plant (31) makes sugar; (32) gives off nitrogen; 
(33) is a solar engine; (34) manufactures proteins and fats by a 
process known as photosynthesis ; (35) gives off oxygen in sunlight. 

VIII. Dicotyledonous stems (36) grow from a thin layer called 
cambium ; (37) show annual rings of growth ; (38) have a large area 
of pith and a rind ; (39) pass foods downward through the sieve tubes 
just outside the cambium ; (40) contain pith rays. 

IX. Monocotyledonous stems (41) have scattered fibrovascular 
bundles; (42) grow by having these bundles arranged in a ring, 
growth taking place from the cambium; (43) have a strong rind 
formed of bundles and epidermis ; (44) contain medullary rays ; 
(45) have annual rings. 

X. Stems (46) are pathways for food and water; (47) owe their 
strength to the tough walls of the cells of which they are composed; 
(48) might be called organs of circulation and support; (49) may be 
modified into leaves; (50) may be modified into tendrils to help in 
climbing. 

Achievement Test 

1. How can you devise an experiment that would show the amounts 
of wa»ter which various soils can hold ? 

2. What are root hairs, where are they found, and what do they do ? 

3. How can you prove that root hairs give off an acid? 

4. How can you devise an experiment to illustrate the principle of 
osmosis ? 

5. How can you show that the sun affects the direction of growth 
of a green plant? 

6. How can you make a diagram to show the cell structure of a leaf ? 

7. How can you prove by experiment what factors are necessary for 
sugar-making in a green plant ? 

8. What are the chief differences in the structure of monocoty- 
ledonous and dicotyledonous stems? 

9. How can you prove that water or food passes up and down in a 
stem? 



REFERENCES 175 

10. How can you devise experiments to prove that food in a root 
has to become soluble before it can pass to another part of the plant ? 

11. What are the functions of the various parts of a living plant? 

Practical Problems 

1. Show why a region well supplied with trees is more likely to have 
frequent rains than a desert region. 

2. Explain fully how you are dependent for your food upon grass. 

3. Make a table in your notebook to show how raw food materials 
get into a green plant, just where each goes, and what becomes of it, 
what results, and what by-products are passed off. Use colors. 

4. Sum up the differences between dicotyledonous and monocoty- 
ledonous plants. 

Useful References 

Dana, Plants and Their Children. Pp. 99-129. (American Book 

Company.) 
Duggar, Plant Physiology. (The Macmillan Co. 1921.) 
Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. (American 

Book Company.) 
Gager, General Botany. (P. Blakiston's Son & Co. 1926.) 
Hodge, Nature Study and Life, Chapters IX, X, XI. (Ginn & 

Co.) 
Transeau, General Botany. (World Book Co. 1923.) 













42Kjjgf*v 




^W;\ 




SloP* 








S.i^: 


p. 


^P" 


w^ff 


jjgjlhiV' 


v|flHflM 


^J^fx 








SURVEY QUESTIONS 


What is relation of cactus wrens (above) to cactus plant ? How many 
different plants can you identify? Do you know how to use a key in 
order to identify new ones ? Do you know in what groups of plants the 
common trees belong? Can you tell how a fern reproduces ? How does 
a tree ? Do you know any plants that are distinctive to your locality ? 



Photo by Wright Pierce 



176. 






PART III. RELATIONSHIPS AND INTER- 
RELATIONSHIPS OF LIVING THINGS 

UNIT VII 

THE PLANT WORLD. HOW DOES IT AFFECT 
MANKIND? 

Preview. Every boy or girl who takes hikes in the open fields, 
along streams, or on a mountain cannot help noticing tremendous 
numbers of different plants and animals of which he does not 
know the names. Every walk I take up a canyon or along a stream 
brings me in contact with some plants or animals I do not know 
by name. But I have considerable satisfaction in knowing that 
if I do see a form new to me I can, in all probability, identify it. 
If I take the specimen home to my library and compare it with 
certain pictures and descriptions that are found in reference books 
of classification, I may be able to name my specimen. This 
identification is made possible by biologists who decided that it 
was necessary to give names to things in order to place them 
correctly in the plant or animal world and, over a period of years, 
have worked out appropriate names. At first such names were 
short descriptions in Latin, which was the universal language 
of scholars. Then a young Swede named Linnaeus, who lived 
during the eighteenth century, made up a system of shorter 
names, which enabled the naturalist more easily to identify and 
namethe specimen. Just as you or I have a family name and a 
given name, so Linnaeus gave plants and animals two names, the 
specific and the generic. This means very little until we know 
that all animals and plants may be placed in groups, of which the 
members have common characters which distinguish them from all 
other plants or animals. Such groups we call species (spe'shez). 

177 



178 THE PLANT WORLD 

A group of different species all of which showed general relation- 
ships to one another might be called a genus (je'mts). The specific 
name corresponds to the given name and the generic to the family 
name, but the generic name is always placed first as my name is 
printed, Hunter, George W., in the telephone book. 

But what is the use of all this, you ask. One very large division of 
the study of biology, that of taxonomy or classification, depends upon 
an understanding of the use of scientific terms used by Linnaeus and 
his followers. We want to be able to place all plants and animals 
in the places they belong in the tree of life. To the average boy 
or girl, who enjoys field trips and who likes to collect specimens, a 
superficial knowledge of the great groups of plant and animal life 
is enough. But days and years of hard work may be necessary be- 
fore the scientist masters enough knowledge to enable him to know 
how to classify all living things correctly. Fortunately for the 
layman, our museums, botanical gardens, and zoological parks have 
specimens of various kinds, but in order to get much pleasure out 
of such a visit he should be able to recognize at least the principal 
plant and animal groups. The pages that follow are written be- 
cause every citizen should have some knowledge along these lines. 

In addition to the pleasure of knowing the names of plants there 
is satisfaction in learning something about their life histories, the 
place they occupy in nature's scale of life, and best of all, we can 
learn something about the good or harm some of these forms do to 
mankind. 

Look at the enormous damage done to crops each year by 
parasitic fungi such as molds, mildews, rusts, and other plant 
diseases. Black stem rust alone costs some of the wheat- 
raising states in a single year almost as much as they put into 
their state system of public instruction for that year. And yet, 
paradoxical as it seems to say it, some of these plants add much 
to man's comfort and control the future of man's expansion on the 
earth. What would we do without yeast to make our bread rise 
or give us commercial alcohol? And how much we enjoy the 
flavor imparted to certain foods by molds. 

Man is dependent primarily on the world's crops and the world's \ 
crops are dependent upon the amount of raw materials m the i 



PLANTS ARE PLACED IN GROUPS 179 

ground used by plants in food manufacture. Nature's law tells 
us that food cannot be made without certain raw materials. One 
of the basic elements needed in protein food manufacture is 
nitrogen, which is present in the air but is not available for use. 
One kind of bacteria is able to take it from the air, nature's store- 
house, and to fix it in a form usable by green plants. These nitrogen- 
fixing bacteria are among man's best friends. 

PROBLEM I. HOW DO WE CLASSIFY PLANTS? 

Laboratory Exercise. Collect a number of common plants in flower 
at the time you take this work, and see if, by using the information you 
find later on in this unit, you can identify them. Use all the help you 
can get, such as simple keys which are found in any good botany or in 
popular books on identification of flowers. 

Plants are placed in groups. If we plant a number of pea seeds 
so that they will all germinate under the same conditions of soil, 
temperature, and moisture, the seedlings will differ one from 
another in a slight degree. But in a general way they will have 
many characters in common, such as the shape of the leaves, the 
length of tendrils, and the form of the flower and of the fruit. More- 
over, if the seeds from these peas are planted, they in turn will 
give rise to plants which will closely resemble the parent plants 
from which the seeds came. Such plants are said to belong to the 
same species. A species is a small group of plants or animals hav- 
ing certain characteristics in common that make them different 
from all other plants or animals. Similar species are placed 
together in a larger group called a genus (plu. genera). For 
example, many species of peas — the wild peas, beach peas, sweet 
peas, and many others — are all grouped in one genus called 
Lathyrus (lath'i-rws) because they have certain structural char- 
acteristics in common. 

Practical Exercise 1. Give a good definition of a species ; of a genus. 

Genera of plants or of animals are brought together in still 
larger or more inclusive groups, the classification being based on 
general likenesses in structure. Such plant and animal groups 
are called, as they become successively larger, family, order, class, 
and phylum. This is called a system of classification. 



180 



THE PLANT WORLD 



Classification of plants. Four great divisions or phyla of the 
plant kingdom are : the Thallophyta (tha-lof i-td), known as thallus 
plants, which do not have roots, stem, or leaves ; the Bryophyta 



5PERKAT0PHYTA 
produce I 
seeds i 



PTER1D0PHYTA 

ferns 



ARTHR0P0DA CHORBATA 

crustaceans I man, 
insects I mammals 

"K0LLU5CA 

clams 



ANNELIDA 

5egmentecCvorms< 

PJtATrKELMlNTrK 

flatvorms 



BRYOPHyTA 

mosses 




ECK1N0DERKATA 

Starfish- 

NEMATHELN1NTHE5 
J roundworms 



COELENTERATA 

* hydra 

-pORIF£PA x 



PROTOZOA 



simple^ 
animals- 



THALLOPHYTA 
simple plants 



All plants and animals developed from a common ancestor and are 
classified under the phyla given in the above diagram. 

(bii-of'i-td), which include the mosses; the Pteridophyta (ter'i- 
dof'i-td), which include the ferns; and the Spermatophyta (spur'- 
md-tof'i-td), which embrace the seed-producing plants. 

Practical Exercise 2. Of what use is a system of classification? Write a 
brief paragraph on this subject. 



Self-Testing Exercise 

Plants and animals may be placed in groups based on (1] 

A group containing individuals which are (2) in (3) 

and which will (4) others of the same kind is called a 

(5). Species are placed in a (6) and more (7) group, 

which is called a (8) . These groups in turn are placed in 

still larger groups, called, as they grow more inclusive, (9), 

(10), (11), and (12). 



HOW WE GET BACTERIA FOR STUDY 181 

PROBLEM H. WHAT ARE BACTERIA AND WHERE ARE 
THEY FOUND? 

The simplest plants, called thallophytes (Lat. thallus, young' 
branch; Gr. phyton, plant), have many forms. They may be 
single-celled or many-celled. They may or may not have chloro- 
phyll, but they never possess the organs of root, stem, and leaves 
found in the higher plants. 

The bacteria are probably the smallest and simplest in structure 
of all the organisms. They are usually classified as thallophytes. 
They have cell walls but do not have any chlorophyll, and are 
therefore not able to manufacture their own carbohydrate food. 

How bacteria were discovered. As early as 1683 Leeuwen- 
hoek is believed to have seen bacteria with his newly invented 
microscope. But it was not until 1865 that Louis Pasteur, the 
famous Frenchman, discovered the relation between bacteria and 
disease in silkworms. Pasteur had shortly before this proved 
that bacteria caused fermentation and that when floating germs 
got into nutrient fluids such fluids would " go bad " and would 
decay. Pasteur and Robert Koch, one in France, the other in 
Germany, were the first people to actually apply the idea of pro- 
tecting animals against disease by inoculating them with injec- 
tions of a culture of weakened organisms that caused the disease. 
Pasteur made this application to man in his treatment for the 
prevention of rabies or hydrophobia. 

Demonstration 1. To prepare and sterilize culture media. To a 
100 c.c. of hot filtered beef broth add 1^ grams of the seaweed agar- 
agar. If agar cannot be obtained, use gelatin. Add a little baking 
soda, if necessary, so that the liquid is faintly alkaline. Boil the mix- 
ture and filter through several layers of absorbent cotton into a sterilized 
Erlenmeyer flask. Close the mouth of flask securely with a plug of 
cotton and boil flask half an hour in a sterilizer. If the agar mixture is 
not clear, it should be filtered again. 

Pour the hot nutrient agar into Petri dishes which have been 
sterilized with dry heat for several hours. Keep Petri dishes in a dry 
place r free from dust until ready to use them. 

How we get bacteria for study. To obtain cultures of bacteria 
for study, it is first necessary to find some material in which they 
will grow, then to kill all living matter in this food material by 



182 



THE PLANT WORLD 



heating it to the boiling point (212° Fahrenheit ) for half an hour 
or more lathis is one method of sterilization), and finally to protect 
the culture -medium, as this food is called, from other living things 
that, might feed upon it. 

Many bacteria thrive in a mixture of beef extract and gelatin 
or agar-agar, a substance derived from seaweed. This mixture, 
after sterilization, is poured into flat sterilized dishes with loose- 
fitting covers. These Petri dishes, so called after their inventor, 
are the traps in which we collect and study bacteria. 

Demonstration 2. Making a pure culture of bacteria. Transfer from 
an infected and incubated culture medium some bacteria on point of a 
sterile needle to the sterile surface of a Petri dish which contains sterile 
agar. Watch the growth of the colonies for several days. Are these col- 
onies all alike in appearance? 

How we may isolate bacteria of one kind from the other. In 

order to get bacteria of a given kind to study, it becomes necessary 
to grow them in what is known as a pure culture. This is done 

after first growing the bacteria in 
some medium such as beef broth 
or gelatin, or on potato. When 
the colonies of bacteria appear or 
the beef broth becomes cloudy, 
one form may be isolated from 
the others by the following proc- 
ess. A platinum needle is first 
passed through a flame to steri- 
lize it. After the needle is cooled 
it is dipped in a colony contain- 
ing the kind of bacteria we wish 
to study. The needle is then 
quickly drawn across the surface 
of a dish of sterile culture medium, 
and the dish is immediately 
covered to prevent any other 
forms of bacteria from entering. When we have succeeded in 
growing only one kind of bacteria in a given dish, we have a pure 
culture. 




Each spot on this culture medium indi- 
cates a colony of bacteria. The different 
sizes and shapes of the spots show that 
there might be more than one type of bac- 
teria present. How could you make a 
pure culture, that is, one containing only 
one kind of bacteria, if you have a steri- 
lized culture medium and this Petri dish 
containing colonies of bacteria ? 



SIZE AND FORM 



183 



Laboratory Exercise. Observe under a compound microscope the 
various forms of bacteria seen in Petri dish of agar which has been ex- 
posed to the air. Make drawings of these bacteria. 

Size and form. In size, bacteria are the most minute plants 



known. A bacterium of average size is about 



500 



of an inch in 
Some species 



bacilli 



length, and perhaps 2 sooo of an inch in diameter, 
are much larger, others smaller. They 
are so small that several million are 
often found in a large drop of impure 
water or sour milk. Three well-defined 
forms of bacteria are recognized : a 
spherical form called a coccus; a rod- 
shaped bacterium, the bacillus; and a 
spiral form, the spirillum. Some bac- 
teria are capable of movement when 
living in a fluid. Tiny lashlike threads 
of protoplasm called flagella project 
from the body, and by a rapid move- 
ment cause locomotion. Bacteria re- 
produce with almost incredible rapidity. 
It is estimated that a single bacterium, 
by a process of division called fission, 
might, if unchecked, give rise to nearly 
17,000,000 others in twelve hours. 
Under unfavorable conditions bacteria 
stop dividing and form rounded bodies called spores. The spore 
is usually protected by a wall and can withstand very unfavor- 
able conditions of dryness or heat ; even boiling for several minutes 
will not kill some forms. 




How would you describe the dif- 
ferent kinds of bacteria? How do 
they move about ? 



Laboratory Exercise. To determine some places where bacteria 
may be found. Expose a number of Petri dishes containing nutrient 
agar for 3 minutes each in as many of the following conditions, and 
as many others, as possible : 

(a) to the air of the schoolroom. 

(b) in the halls of the school while pupils are passing. 

(c) in the halls of the school when pupils are not moving. 

(d) at the level of a dirty and much-used city street. 

(e) at the level of a well-swept and little-used city street. 



184 



THE PLANT WORLD 



(/) in a city park. 

(g) in a factory building. 

(h) to dirt from hands. 

(i) to contact with scrapings from the interior of the mouth. 

(j) to contact with decayed vegetable or meat. 

(k) to contact with dirty coin or bill. 

(I) to contact with two or three hairs from a pupil's head. 

Cover the dishes securely and place them in a warm dark place. 

After three to five days, note the conditions of the various plate 
cultures. Each day count the number of spots (colonies) of bacteria 
and molds growing on the culture medium. Make a table to show 
your results. 



Petei Dish Exposed 


Number of Colonies of Bacteria 


1st 
Day 


2nd 
Day 


3rd 
Day 


4th 
Day 


5th 
Day 


6th 
Day 


7th 
Day 


8th 
Day 


(a) Air of schoolroom 


















(6) Busy halls of school 


















(c) Quiet hall of school 


















(d) Busy city street 


















(e) Etc. 



















Where are bacteria found in abundance? What are the factors in 
your environment by means of which bacteria may get to your body? 
Is it true that " bacteria are found anywhere but not everywhere "? 



Where bacteria are most numerous. As the result of our 
studies, we may draw some inferences concerning the presence of 
bacteria in our own environment. They are evidently present j 
in all air, and in greater quantity in air that is moving than in j 
quiet air. Why ? That they stick to particles of dust was proved 
by exposing a sterile culture dish in a schoolroom. Bacteria are 
present in great numbers where crowds of people live and move. 
The air from dusty streets of a populous city contains more bac- 
teria than does the cleaner air of a village street. The air of a 
city park contains relatively few bacteria when compared with the 



WHERE BACTERIA ARE FOUND 



185 




Growth of bacteria in an impure drop of water 
placed on a sterilized culture medium. 



air of a near-by street ; the air of the woods or high mountains 
contains fewer still. Why ? 

Fluids the favorite home of bacteria. Tap water, standing 
water, milk, vinegar, wine, cider, all can be proved to contain 
bacteria by experiments similar 
to those already suggested. 
Spring or artesian well water 
would have very few, if any, 
bacteria, while the same quan- 
tity of river water, if it held 
any sewage, might contain un- 
told millions of these little 
organisms. 

Individual Project. Deter- 
mine by experiment whether bac- 
teria will grow without fluids being 
present. Try dry and moist beans. 

Demonstration 3. To deter- 
mine the foods most favorable 
for the growth of bacteria. 

Materials. Raw meat, cooked meat, white of egg, beans, Indian 
meal flour, cake, sugar, butter, test tubes, and absorbent cotton. 

Method. Moisten all of the above food substances. Place small 
particles of them in test tubes with a little distilled water. Expose all to 
the air for half an hour. (This can be done during a class period.) Plug 
the tubes with absorbent cotton and allow to stand for several days. 

Note the appearance and odor of the various substances after five 
days. 

In which substances was there rapid growth of bacteria ? 

Food of bacteria. Bacteria, since they contain no chlorophyll, 
are unable to make carbohydrate food, but must absorb their 
foods, ready formed, from decaying organic matter. Some bacteria, 
however, seem able to build up the protein, which they need for 
growth, out of absorbed carbohydrates and simple inorganic nitrog- 
enous substances. 

What bacteria do to foods. When bacteria feed, they digest 
the food substances by means of enzymes which they secrete. 
The food is decomposed and eventually rots. The material left 
behind after the bacteria have finished their meal is quite different 
from its original form. It is broken down by the action of the 



186 THE PLANT WORLD 

bacterial enzymes into gases, fluids, and some solids. It has an 
offensive odor, and contains poisons which come as a result of the 
work of the bacteria. 

Demonstration 4. To show how light affects the growth of bacteria. 

Cover with black paper one of two Petri dishes in which bacteria 
are growing. Place the dishes in a light warm place for a few days. 
Compare the growth of bacteria in the exposed dish with the growth 
in the covered dish. 

Bacteria and air. We have seen that plants need oxygen in 
order to perform the work that they do. This is equally true of 
all animals. But not all bacteria need air to live ; in fact, some 
are killed by the presence of air. Bacteria which live without free 
oxygen are called anaerobic bacteria. They need oxygen, as do all 
other living things, but they obtain it by breaking down the foods 
on which they live, and utilizing the oxygen freed in this process. 
Those that grow or thrive in the presence of oxygen are called 
aerobic bacteria. 

Self -Testing Exercise 

Bacteria are found almost (1). Bacteria can be obtained 

for study by exposing a (2) medium containing (3) 

to the (4) for a few minutes. Under proper conditions of 

(5) they grow rapidly. There are three common (6) 

of bacteria : the (7) form, called coccus, the (8) ba- 
cillus, and a (9) form, the spirillum. They prefer (10) 

to all other food. Many forms are (11) by (12) 

to light. Some forms obtain their (13) by breaking down 

the food substances on which they live. 



PROBLEM III. WHAT ARE SOME USEFUL THINGS THAT 
BACTERIA DO? 

Bacteria cause decay. Imagine a world cluttered up with dead 
plants, dead animals of all kinds, dead bodies of fish in the waters, 
insects in the grass, cattle in the fields. Did you ever think 
what this world would be like if nothing could decay? Bacteria 
are responsible for decay. These bacteria are most numerous in 
rich, damp soils containing large amounts of organic material. 



USEFUL BACTERIA 



187 



They are useful because they feed upon dead bodies of plants and 
animals which otherwise would soon cover the surface of the earth 
to the exclusion of everything else. Bacteria may be considered 
scavengers. They oxidize organic materials, changing them to 
compounds that can be absorbed by plants and used in building 
protoplasm. Without bacteria it would be impossible for life to 
exist on the earth, for green plants would be unable to get the raw 
food materials in forms that they could use in making food and 
living matter. 

Relation of bacteria to fermentation. Bacteria continue the 
process of fermentation begun by the yeasts. In making vinegar 
the yeasts first make alcohol which the bacteria change to acetic 
acid. The lactic-acid bacteria, which sour milk by changing the 
milk sugar to an acid, are useful when they sour the milk for the 
cheese maker. 

Other useful bacteria. Certain bacteria give flavor to cheese 
and butter, others give flavor to sauerkraut, while still other 
bacteria aid in the 

" curing " of to- /. . V- — ^ --/ . _\ 

bacco, in the prep- 
aration of the 
dye indigo, in the 
".retting " or fer- 
mentation of cer- 
tain fibers of plants 
for the market, as 
hemp, flax, and 
ramie, in the rot- 
ting of animal mat- 
ter from the skel- 
etons of sponges, 
and in the process 
of tanning hides 
to make leather. 

Relation of bac- 
teria to free nitrogen. It has been known since the time of the 
Romans that the growth of clover, peas, beans, and other legumes 



[ plcc nts 1^ fccni metis J 

/ of decccW fcoeteri 




lxxe thrice 



Explain from the text and diagram what is meant by the nitrogen 
cycle. What is the value of nitrogen-fixing bacteria ? 



188 



THE PLANT WORLD 




wootule enlargecC 




causes soil to become more favorable for the growth of other 
plants, but the reason for this has been discovered in late years. 
On the roots of the plants mentioned are found little nodules 

or tubercles; in each 
nodule exist millions 
of bacteria, which 
take nitrogen from 
the air in the soil and 
build it into nitrites 
which are converted 
by other bacteria 
into nitrates. In this 
form it can be used 
by the plants. Only 
these bacteria, of all 
living plants, have 
the power to take 
free nitrogen from 
the air and make it 
over into a form that 
can be absorbed by 
the roots. They live in a symbiotic l relationship with the plants 
on which they form tubercles, for the legumes provide them with 
organic food. All the compounds of nitrogen are used over and 
over again, first by plants, then as food by animals, eventually 
returning to the soil again, or in part being released as free nitro- 
gen ; but any new supply of usable nitrogen must come by means 
of these nitrogen-fixing bacteria. 

Rotation of crops. The facts mentioned above are made use 
of by progressive farmers who wish to produce as large crops as 
possible from a given area of ground. Plants that are hosts 
for the nitrogen-fixing bacteria are raised early in the season. 
Later these plants are plowed in and a second crop of a different 
kind is planted. The latter grows quickly and luxuriantly because 
of the nitrates left in the soil by the bacteria which lived with the 

1 symbiotic (sim'biofik) : The living together in intimate association of two dis- 
similar organisms. 



section, throurfk 
ce nocUxle 



bacteria fcunct wi_- 
Cells of a nodule/ 

Explain by use of this diagram where the nitrogen-fixing 
bacteria live. 



ROTATION OF CROPS 



189 



first crop. For this reason, clover is often grown on land in which 
it is proposed to plant corn later, the nitrates left in the soil giving 
nourishment to the young corn plants. In well-managed farms, 
different crops are planted in succession in a given field in different 
years so that one crop may replace some of the elements taken from 
the soil by the previous crop. This is known as rotation of crops. 1 
Five of the elements necessary to the life of the plant which 
may be taken out of the soil by constant use are calcium, nitrogen, 
phosphorus, potassium, and sulphur. Several methods are used 
by the farmer to prevent the exhaustion of these and other raw 
food materials from the soil. One method, known as fallowing, 
is to allow the soil to remain idle until bacteria and oxidation have 
renewed the chemical materials used by the plants. This is an 
expensive method if land is high priced. The more common 
method of enriching 
soil is by means of fer- 
tilizers and materials 
rich in plant food. 
Manure is most fre- 
quently used, but 
many artificial ferti- 
lizers, most of which 
contain nitrogen in the 
form of some nitrate, 
are used because they 
can be more easily 
transported and sold. 
Such are ground bone, 
guano (bird manure), 
nitrate of soda, and 

many others. Most Is this a g00d plan for rotating crops ] 

fertilizers contain other important raw food materials for plants, 
especially potash and phosphoric acid. Both of these substances 
are made soluble by the action of the carbon dioxide in the soil, 
and in this form they can be taken into the roots. 

1 Crop rotation is not only a process to conserve the fertility of the soil, but 
also a sanitary measure to prevent infection of the soil. 




Why? 



190 THE PLANT WORLD 

Practical Exercise 3. What are the direct values of bacteria to (1) market 
gardening; (2) fruit raising ; (3) manufacturing? 

Self-Testing Exercise 

Bacteria which cause (1) are useful. More and better 

crops are made possible through the (2) (3) bacteria. 

Bacteria are used in the processes of (4) fibers of plants, 

(5) of hides, (6) tobacco, and giving (7) 

to some animal products. 

PROBLEM IV. WHAT ARE YEASTS AND WHAT DO THEY DO? 

Fermentation. It is of common knowledge that the juice of 
fresh apples, grapes, and some other fruits, if allowed to stand 
exposed to the air for a short time, will ferment. That is, the 
sweet juice will begin to taste sour and to have a peculiar odor, 
which we recognize as that of alcohol. The fermenting juice 
appears to be full of bubbles which rise to the surface. If we 
collect enough of the gas in these bubbles to make a test, we find 
it is carbon dioxide. 

Evidently something changed some part of the apple or grape, 
namely, the sugar (C 6 Hi 2 6 ), into alcohol (C 2 H 5 OH) and carbon 
dioxide (CO2). This chemical process is known as fermentation. 

Home Experiment. To determine the conditions favorable for the 
growth of yeast. Label three pint fruit jars A, B ; and C. Add one 
fourth of a compressed yeast cake to two cups of water containing two 
tablespoonfuls of molasses or sugar. Stir the mixture well and di- 
vide it into three equal parts and pour into the jars. Place covers 
on the jars. Put jar A in the ice box on the ice and jar B over the 
kitchen stove or near a radiator. Heat jar C by immersing in a pan 
of boiling water, and then place it next to B. After forty-eight hours, 
see if bubbles have made their appearance in any of the jars. 

Which jars, if any, show bubbles on the surface? Describe the 
conditions which favor the growth of yeast. Explain how you know 
that yeast has grown. 

Yeast. If a small piece of compressed yeast cake is shaken 
up with some molasses and water and the mixture allowed to 
stand overnight in a warm place, fermentation will take place. 
Examination of a drop of the settlings from the mixture shows that 
the common compressed yeast cake contains millions of tiny yeast 



COMMERCIAL YEAST 



191 



plants. In its simplest form a yeast plant is a single cell, ovoid 
in shape and usually containing one or more vacuoles. The cells 
reproduce by a process called budding. Under certain conditions 
spores are found. 

An enzyme causes fermentation. It has been proved that if 
yeast cells are ground up until they are destroyed, the juice 
filtered from them is able 
to cause fermentation. 
Similar experiments have 
been made with bacteria, 
showing that enzymes 
formed within the cells 
cause fermentation. 
These enzymes are called 
zymases. 

Commercial yeast. 
Cultivated yeast is now 
supplied in compressed 
or dried yeast cakes. In 
both cases the yeast 
plants are mixed with 
starch and other sub- 
stances and pressed into a cake. The compressed yeast cake must 
be used fresh, as the yeast plants begin to die rapidly after two or 
three days. The dried yeast cake contains a much smaller number 
of yeast plants, but is probably more reliable if the yeast cannot 
be obtained fresh. 




Life history of yeast. Follow the arrows and work out 
what happens after the germination of the spores. How 
many spores are produced in the sac or ascus shown at the 
bottom of the diagram? 



Home Experiment. To determine the conditions favorable for the 
growth of yeast in bread. Make a small amount of dough by mix- 
ing flour, sugar, salt, and water in proportions to make a thick paste. 
Knead with a little yeast which has previously been mixed with 
water. Now place one lot of dough in the ice box, one at the tem- 
perature of the room, and one in a warm place (over 95° F.). Later 
bake 'each lot and use in the laboratory. 

Which of the three lots has risen the most? Which, after baking, 
has the best appearance? The best taste? What makes the holes 
in the bread ? 

What caused the dough to rise ? What are the best conditions for 
this to take place ? Will the mixture rise if no yeast is added ? Why ? 



192 



THE PLANT WORLD 







O , 
i§ ctioxicCe 



Bread making. Most of us are familiar with the process of 
bread making. The materials used are flour, milk or water, or 
both, salt, a little sugar to hasten the process of fermentation, or 
" rising," as it is called, some butter or lard, and yeast. 

After the materials are mixed thoroughly the bread is put aside 
in a warm place (between 70°-75° Fahrenheit) to " rise." If we 

examine the dough 
after a few hours, we 
find many holes in it, 
which give the mass 
a spongy appear- 
ance. The yeast 
plants, owing to 
favorable condi- 
tions, have grown 
rapidly and made 
bubbles of carbon 
dioxide. Alcohol is 
present, too, but 
this is evaporated 
when the dough is 
baked. The baking 
cooks the starch of 
the bread, drives off 





flour 
crater ondi 
yeast 



is bcckect 

Explain the process by which bread becomes light ? 



the carbon dioxide and alcohol, and kills the yeast plants, besides 
forming a protective crust on the loaf. 

Sour bread. In the " rising " of bread, bacteria always do 
part of the work of fermentation. Certain of these plants form 
acids after fermentation takes place. The sour taste of the bread 
is usually due to this cause, and may be prevented by baking the 
bread before the acids form, by having fresh yeast, good fresh 
flour, and clean vessels with which to work. 

Importance of yeasts. Since yeast cells do not contain chloro- 
phyll they cannot make their own food but must get it already 
made. Their food consists mostly of fruit juices and other sugar 
solutions. If a fruit syrup is left exposed to the air wild yeast 
plants will settle on it, and multiply rapidly, causing fermentation. 



TO LEARN ABOUT SOME DESTRUCTIVE FUNGI 193 

They may get into canned substances put up in sugar and cause 
them to " work," giving them a peculiar flavor. But they can be 
easily killed by heating to the temperature of boiling. On the other 
hand, yeast gives us leavened bread. 

Many interesting experiments with yeast may be tried as home 
projects. For excellent suggestions, see Conn's Bacteria, Yeasts, 
and Molds in the Home, pp. 274-278. 

Practical Exercise 4. How may yeasts be useful to man ? Where are yeasts 
found? Give proofs. What products are formed when bread rises? What 
becomes of these products? It is said that yeast plants are at once the 
friends of man and yet make him their slave. Explain what this means. 

Self-Testing Exercise 

Yeasts cause (1) by changing (2) into (3) 

(4) and (5) . An enzyme called (6) causes 

fermentation (7) also cause bread to rise, because of the 

bubbles of (8) (9) formed during their (10) 

growth when the (11) is put in a (12) place. 

PROBLEM V. TO LEARN ABOUT SOME DESTRUCTIVE FUNGI 

Most of us are familiar with some fungi, as the edible mushrooms 
and the so-called " toadstools " found in parks or lawns. We 




L. W. Brownell 
These poisonous toadstools (amanita muscaria) are found during the summer and early 
autumn along roadsides near trees, in groves, and in woods. 



194 



THE PLANT WORLD 




Chestnut blight. The dead trees along this road have 
been attacked by the parasite. 



have already seen some- 
thing of their characteris- 
tics. They are as much 
dependent upon the green 
plants for food as are ani- 
mals. But some of the 
fungi require dead organic- 
matter for their food. 
This may be obtained from 
decayed vegetable or ani- 
mal material in soil, from 
the bodies of dead plants 
and animals, or even from 
foods prepared for man. 
Fungi which feed upon 
non-living organic material 
are known as saprophytes. 
Examples are the mush- 
rooms, yeasts, and molds. 
Some parasitic fungi. Some fungi prefer living plants or animals 
for their food and are therefore classed as parasites. An example 
is the chestnut blight or canker, which has killed chestnut trees 
by the thousands in the eastern part of the United States. It pro- 
duces millions of tiny spores, which, blown about by the wind, 
light on the trees, sprout, and send under the bark thread-like 
mycelia which absorb the food circulating in the living cells, even- 
tually causing the death of the tree. The chestnut canker, in- 
troduced from abroad on chestnuts planted near the city of New 
York in 1904, within ten years had destroyed practically every 
chestnut tree in the eastern part of the United States. 

Another fungus which does much harm to trees is the shelf or 
bracket fungus. The shelflike body is in reality the reproductive 
part of the plant; in its lower surface are formed millions of 
asexual spores, which, when they fall on a dead or a dying tree 
trunk, may start a new fungus growth. The true body of the 
plant, a network of threads, is found under the bark. Once 
established, it spreads rapidly. There is no remedy except to 



BLACK STEM GRAIN RUST 



195 




Brownell 



Shelf fungi (Fomes applanatus as often seen growing on the 
trunks of trees. They cause enormous losses by causing the 
timber to decay. 



kill the tree and burn it, so as to destroy the spores. Each year 
many fine trees, sound except for a slight bruise or other injury, 
are infected and 
eventually killed 
by this fungus. 

Field Exercise. 

On a field trip we 
may see a number of 
trees which are in- 
fected with fungi. 
Count the number 
of perfect trees in a 
given area. Com- 
pare it with the 
number of trees at- 
tacked by fungus. 
Does the fungus ap- 
pear to be trans- 
mitted from one tree 
to another near 
at hand? In how 
many instances can you discover the point where the fungus first at- 
tacked the tree? How do the spores leave the spore case? How do 
they germinate on the tree which they attacked? 

Black stem grain rust. Wheat rust is probably the most destruc- 
tive parasitic fungus. For hundreds of years this rust has been 
the most dreaded of plant diseases, because it destroys the one 
harvest upon which the civilized world is most dependent. For 
a long time past the appearance of rust has been associated with 
the presence of barberry bushes in the neighborhood of the wheat 
fields. Although laws were enacted in 1760 in New England to 
provide for the destruction of barberry bushes near infected wheat 
fields, nothing was" actually known of the relation existing be- 
tween the rust and the barberry until comparatively recent years. 
It has now been proved beyond doubt that the wheat rust 
passes' part of its life as a parasite on the common barberry and 
from there gets to the wheat plant, where it undergoes a compli- 
cated fife history. The wheat leaf, its nourishment and living 
matter used as food by the parasite, soon dies, and no grain is 
produced, 



196 



THE PLANT WORLD 



It is estimated that in the grain-raising states of the Middle West 
668,338,000 bushels of grain have been destroyed by black stem 
rust in the 13 years from 1915 to 1927 inclusive. This has meant a 
yearly average loss of almost $55,000,000. The only way to prevent 
this pest is to break the chain of the life cycle by destroying the 
barberry bushes on which the spores grow in the spring of the year. 





recC spore 
Hovm to 
another stem 

Ted or 

summer- 
rust on 
M/heat stem 



barberry rust 

spore infecting* 

the cells ; of -wheat 

stem in 

Spring- 



through 
ctSfaino; 



breo-t 
pore. 



recTnrst , 

from stem fe steroJ 
cCtrriMg" sum met* 

blorck or 
-winter rust/ 
lives on l 

straw through j 





infection fornix y@), S" ■■" v ?pL ^J~ If v-^-^ <-««-^ 
^^^^V -^Li O .lfir^in S | 0r<l 
a cluster cup •V^** ' JJ^-v ^y V bocfxes , soorida 

^S&O a sporidium 
W^T° infects the 
jf cells of or 

barberry leaf. 

The life history of wheat rust. How would you go to work to exte 
this pest ? Explain. 



te 



Blister rust. The pine tree blister rust is a recent importation 
from Europe that threatens our white pine forests. This rust 
passes one stage on the currant and gooseberry, so that the only way 
to control it is to remove all currant and gooseberry bushes from 
the neighborhood of such trees. 

Mildews. Another group of fungi that are of considerable 
economic importance is made up of the sac fungi. Such fungi 
are commonly called mildews. Some of the most easily obtained 



MILDEWS 



197 



specimens come from the lilac, rose, or willow. These fungi do 
not penetrate the host plant to any depth, but cover the leaves of 
the host with the whitish threads of the mycelium. Hence they 
may be killed by means of applications of some fungus-killing 
fluid, as Bordeaux mixture. They obtain their food from the 
outer layer of cells in the leaf of the host. Among the useful 
plants preyed upon by this group of fungi are the plum, cherry, 
and peach trees. The diseases known as black knot and peach 
curl are caused by these fungi. 

Potato wart is another fungus disease which was introduced 
into this country in 1911 and has now spread over the eastern 
part of the United States. It attacks the potato tuber, so that 
the disease may not be noticed until time to harvest the crop. 
Since its spores may be dormant in soil for several years, the only 
way to combat the pest is to rotate other crops on the field as 
well as to destroy all infected tubers. 

GRAIN DESTROYED BY STEM RUST IN THIRTEEN YEARS 
1915 to 1927, Inclusive 



State 

• 


Wheat 
(Bushels) 


Oats 
(Bushels) 


Barley 

and 

Rye 

(Bushels) 


Total 

All 

Grains 

(Bushels) 


Average 

Annual 

Stem Rust 

Losses 

All 
Grains 
(Dollars) 


Total 

Loss 1927 

All 

Grains 
(Dollars) 


Colorado . 
Illinois 
Indiana . 
Iowa . . 
Michigan 
Minnesota 
Montana . 
Nebraska 
No. Dakota 
Ohio . . 
So. Dakota 
Wisconsin 






2,469,000 

4,992,000 

2,974,000 

4,246,000 

6,487,000 

86,002,000 

14,863,000 

18,505,000 

202,316,000 

4,806,000 

76,209,000 

4,456,000 


176,000 
50,156,000 

1,479,000 

33,761,000 

15,831,000 

50,345,000 

221,000 

3,922,000 
14,788,000 

2,694,000 
37,574,000 
10,349,000 


541,000 

353,000 
Trace 
2,143,000 

453,000 
3,498,000 
Trace 

276,000 

4,606,000 

80,000 

4,170,000 

2,417,000 


3,186,000 

55,501,000 

4,453,000 

40,150,000 

22,771,000 

139,845,000 

15,084,000 

22,703,000 

221,800,000 

7,580,000 

117,953,000 

17,312,000 


$ 218,000 

2,275,000 

481,000 

1,580,000 

1,409,000 

11,742,000 

1,154,000 

2,437,000 

22,191,000 

562,000 

9,385,000 

1,109,000 


Trace 
$ 8,707,000 
Trace 
729,000 
765,000 
18,592,000 
Trace 
Trace 
19,075,000 
247,000 
9,297,000 
375,000 


Total . ' . . . . 


428,325,000 


221,386,000 


18,627,000 


668,338,000 


54,543,000 


57,787,000 



These are official estimates of the Plant Disease Survey, Bureau of Plant Industry, United 
States Department of Agriculture. The money value of the grain destroyed in the thirteen- 
year period was $709,081,000, basing calculations on the farm prices for December 1 of each year 
and disregarding any effect the reduced production, caused by rust, may have had on the 
market price. Losses for 1927 are preliminary. 



198 THE PLANT WORLD 

Self-Testing Exercise 

The (1) are plants which are either parasites or saprophytes, 

the latter living on (2) (3) matter and the former on 

(4) plants and animals. The (5) fungi do enormous 

damage to (6) every year. The black stem wheat rust, which 

lives on two (7), (8) and (9), does a yearly 

damage of almost $55,000,000. The pine tree (10) 

(11) is another recent importation from (12). It lives on two 

hosts : the (13) or (14), and the (15). To 

curb the damage from such parasites one of the (16) plants 

must be destroyed. 

PROBLEM VI. WHAT ARE MOLDS? WHAT DO THEY DO? 

Demonstration 5. To determine the conditions favorable for the 
growth of mold. Place pieces of bread in each of four wide-mouthed 
bottles or jars. Add a little water, and expose all four bottles to 
the air of the living room or kitchen for half an hour. Then cover the 
bottles and plunge one into boiling water for a few moments. Place 
this and a second jar side by side in a moderately warm room. Place 
the third jar in the ice box and the fourth in a hot dry place. 

Notice day by day any changes that occur in the contents of the 
jars. In which jar does growth appear first? Do all jars have a like 
growth of mold at the end of a given period of time? 

How does the mold get on the bread? Where does it come from? 
Why did you add water to the jars? What conditions must you have 
for the growth of mold? Conversely, how would you keep molds 
from getting a foothold on foods ? 

Physiology of the growth of mold. Molds, in order to grow 
rapidly, need food, darkness, oxygen, moisture, and moderate heat. 
They obtain their food from the materials on which they live. 
This they are able to do because they have rhizoids l which give 
out digestive enzymes which change the starch of the bread to 
sugar and the protein to a soluble form which can be absorbed by 
the cells. These absorbed foods are then used to supply energy 
and make protoplasm. Thus molds act like animals, except that 
digestion takes place outside of the body. 

What can molds live on ? Molds feed upon all cakes and breads, 
upon meat, cheese, and many raw vegetables. They are almost 
sure to grow upon flour if it is allowed to get damp. Jelly and 
other foods containing moisture are particularly favorable to the 

1 Rhizoids (ri'zoids) : rootlike filaments or threads. 



HOW TO PREVENT MOLDS 



199 



growth of molds. Leather, cloth, paper, or even moist wood will 
give food enough to support their growth. At least one trouble- 
some disease, ringworm, is due to the growth of molds in the skin. 
What mold does to ^ ^• 1 x«_ 

spores Ja|lk sporcer*^***"*- 

foods. Mold usually 
changes the taste of the 
material it grows upon, 
rendering it " musty " 
and sometimes unfit to 
eat. Eventually food 
will be spoiled com- 
pletely because bacterial 
decay sets in. Some 
molds are useful. They 
give the flavor to Gor- 
gonzola, Roquefort, 
Camembert, and Brie 
cheeses. But, on the 
whole, molds are pests 
which the housekeeper 
wishes to get rid of. 

How to prevent molds. As we have seen, moisture is favorable 
for the growth of mold; conversely, dryness is unfavorable. 
Inasmuch as the spores of mold abound in the air, materials which 
cannot be kept dry should be covered. Jelly, after it is made, 
should at once be tightly covered with a thin layer of paraffin or 
waxed paper, which excludes the air and possible mold spores. 
To prevent molds from attacking fresh fruit, the surface of the 
fruit should be kept dry and, if possible, each piece of fruit should 
be wrapped in paper. Why? Mold spores may be killed in a 
few minutes with dry heat at 212° F. Dry dusting or sweeping 
will raise dust, which usually contains spores of mold and bacteria. 
Use a dampened broom or dust cloth frequently in the kitchen, if 
you wish to preserve foods from molds. 




Life history of bread mold. There may be a sexual 
stage in the life history (shown in center of diagram) in 
which the formation of a zygospore results. What value 
might this be to the mold ? 



Practical Exercise 5. Where may mold spores be found ? What must they 
have in order to grow ? On what part of foods do molds grow ? How would 
you prevent mold spores from getting into food ? 



200 



THE PLANT WORLD 



Self-Testing Exercise 

Molds grow under favorable conditions of (1), (2), 

(3), and (4) heat. They spoil many (5) and 

cause (6). Some molds give (7) to cheese. Molds 

may be kept out of food by keeping the food (8) and well 

(9). Molds send out rootlike threads, (10), which give 

off (11) (12) and absorb (13). 



PROBLEM VH. WHAT ARE SOME EXAMPLES OF COMMON 

ALGAE? 

The Fungi which include all the plants which we have so far 
studied in this unit constitute one large division of thallophytes. 
We now come to the other main group, the algae. In the classifi- 
cation given below we find three classes of algae. 

The Algae. The algae are nearly all water plants, although some 
few species may be found on tree trunks and rocks which are exposed 
to moisture. They are a large group of chlorophyll-bearing plants, 
although in some forms the characteristic green color of chlorophyll 
is masked by some other coloring matter, usually red and brown. 
They have many forms, ranging from single cells to filamentous 
colonies or even long ribbon or rope-like masses many feet in length, 
as in some seaweeds. Our attention is called to them in an un- 



Chlorophyceae 



\ / 



.T&aeophy< 

brown / c 



'ceae 

brown J g\£o& 



THALLOPMYTA 




^PWoomycetes-/ Eumycetes \_Phodophyceae 




Jnucor 




yeasts -mushrooms 



red ctigae 



I. The Green algae are of countless forms, unicellular, filamentous, plate-like, and in irregular 
masses of cells. There are both fresh-water and salt-water forms, and others live on land. The 
so-called " Red-Snow" is a form living in snow patches. Pleurococcus and vaucheria are also 
examples. Some 5000 species have been described. 

II. The Brown algae are nearly all marine plants. We know them as seaweeds. About 
1000 species are known. 

III. The Red algae, mostly marine, are our most delicate and beautiful seaweeds. There are 
about 3000 named species. 

IV. The Fungi are without chlorophyll. There are about 75,000 species in all. Many of 
them are harmful. There are two classes: Phy corny cetes, the molds - , and Eumycetes, yeaats, 
mushrooms, and puffballs. Bacteria are usually classed as Fungi. 



SOME EXAMPLES OF ALGAE 



201 





pleasant way at times, when, after multiplying very rapidly during 

the hot summer, they die suddenly in the early fall and leave their 

remains in our water supply. Much 

of the unpleasant taste and odor of 

drinking water comes from this cause. 
Some examples of algae. One of 

the simplest algae is Pleurococcus 

(pl6o-ro-kok'#s). This little plant 

consists of a single tiny cell, which 

by division may give rise to two or 

more cells which cling together in a 

mass. The green color on tree trunks, 

stone houses, etc., is often due to 

millions of these little plants. 

Spirogyra, a pond scum, is known 

to every boy or girl who has observed 

a small pond or sluggish stream. It 

grows as a slimy mass of green threads 

or filaments. Under the low power 

of the microscope, the body is seen to 
be a filament made up of elongated 
cylindrical cells, each of which con- 
tains a spirally wound band of chlo- 
rophyll. Spirogyra may reproduce 
..cytoplcxsm asexually by division of the cells. It 
may also reproduce sexually. When 
this happens, the cells of two adjoin- 
ing filaments push out portions of their 
cell walls which meet, forming a bridge. 
The cell walls in the middle of the 
bridge dissolve. The protoplasm of 
the cells thus joined condenses into 
two tiny spheres, and ultimately the 
contents of one cell passes through 
the connecting tube and mingles with 
the cell of the neighboring filament. 
This process by which two cells of 



eel \/afl 

.— nucleus 
fC^if..chloropla5t 

a single cell 

a colony 
of Wo 
OeMs 

anot 
a colony 
of four 
cells 



Pleurococcus. Explain how a colony 
of Pleurococcus might come into ex- 
istence. 



chlorophyll 
loandL 



.nucleus 



..cell ^ccll 



. ..vacuole 



A single cell of Spirogyra. Is the cell 
flat or round in cross section? 



202 



THE PLANT WORLD 



nearly equal size fuse to form a single cell is called conjugation 
The result of this process of fusion is a thick-walled resting cell 
which is called a zygospore (zl'go-spor). This cell thus formed can 
withstand considerable extremes of heat, cold, and dryness. 
After the zygospore is formed, the cell walls break and the zygo- 
spore falls to the bottom of the pond. Under favorable conditions, 
it will germinate and form a new filament. 

Self-Testing Exercise 

The simplest green plants are the (1). The (2) of 

two cells of nearly equal size to form one cell is called (3) . This 

method of reproduction is characteristic of (4). A 

(5) is a thick-walled resting cell. 



PROBLEM Vm. WHAT IS THE LIFE HISTORY OF A MOSS 

PLANT? 

The Bryophyta consist of two groups of plants, the liverworts 
and the mosses. Both are small plants and nearly all forms live 

on land. They show 
a much greater de- 
velopment of tissues 
than the algae and 
may be either thallus- 
like (liverworts) or 
have stems with 
rootlike projections 
(rhizoids) and very 
simple leaves, as 
the mosses. 

The Moss Plant. 
One of the mosses 
frequently seen and 
easily recognized is 
the " pigeon- wheat " 
moss. A leafy moss 
plant has rhizoids, 

The life history of a moss. Refer to the numbers in your . , 

text and work out the stages in the life history. an Upright Stem, and 




GAMETOPHYTE 203 

green leaves. In the plants which have a stalk and capsule, (1) 
the stalk grows out of the leafy plant. 

Sporophyte. The capsule is the sporangium (2). The stalk 
and capsule together form the sporophyte (spo'ro-fit) or spore- 
producing generation of the moss. 

Gametophyte. The spore (3) germinates into a threadlike pro- 
tonema. The protonema soon develops rhizoids (4), and tiny 
buds appear which form the adult plants. These may grow only 
leaves, or they may develop into plants (5) that bear the rosettes 
of leaves which hold either sperm or egg cells, for these are pro- 
duced on separate plants. These two kinds of plants form the 
sexual generation (called the gametophyte) of the moss (6, 7, 8, 
9). After a sperm has been transferred to the egg cell, fertiliza- 
tion or fusion of these two cells takes place (10). This process 
results in the growth of the sporophyte which bears the asexual 
spores. These spores produce a leafy moss plant which bears 
organs producing eggs and sperms. This life history is known as 
alternation of generations. 

Practical Exercise 6. Why do we call the life history of moss alternation of 
generations ? 



BRYOPHYTA 



HepaticaeV \_M^c^ci 






liver ^^t^fF mo$-$- 

These plants are small and live mostly on land. There are about 16,000 known species. 

Self-Testing Exercise 

Bryophytes include (1) and (2). The mosses 

show (3) of generations in which an (4) stage is 

followed by a (5) stage. A spore gives rise to a (6) 



204 



THE PLANT WORLD 



which produces (7) and . . 

(9) grows into a leafy 

(10) spores. 



. . . . (8). After fertilization an 
moss plant which produces 



PROBLEM IX. WHAT IS THE LIFE HISTORY OF A FERN 

PLANT? 

The pteridophytes are a group which, when the world was 
younger, played a very important part in the vegetation on the 
earth. Some coal is made very largely from their bodies. They 
have true roots, stems, and leaves, but reproduce like the mosses, 
by forming spores. 

Life history of a fern. The common fern begins life as a spore. 
This germinates into a tiny heart-shaped body called a pro- 







■Stbofliui 



The life history of a fern, (it Adult plant, (2) a leaflet showing sori or groups 
of spore cases, (3^ a section through a sorus, (41 a spore case opening, (5) a 
spore which germinates into (6) a prothallium which in turn produces organs 
containing (7) sperms and (8) eggs. When an egg is fertilized it gives rise to 
(9) a new fern plant. 

thallium which contains sex organs holding sperm and egg cells. 
This is called the gametophyte generation of the plant because 



LIFE HISTORY OF A FERN 



205 



it holds the male and female gametes or sex cells. These cells 
after fertilization produce leafy structures (fronds) which bear the 
asexual spores. These spores when ripe germinate and the life 
cycle begins over again, a sexual generation alternating with an 
asexual generation. 

Practical Exercise 7. Compare, by means of labeled diagrams, the life his- 
tories of the moss and fern. 



l^TERIDOPHYTA ] 



Rlicirieaje-/ B^uisetineae^I^copodlneae 




horsetails 




olu fa-rn o&&<2,$ 



These pteridophytes include three classes : the true ferns, the horsetails, and the club mosses. 
There are about 8000 known species. 

Self-Testing Exercise 

The (1) or ferns have (2) of generations in their life 

history. In the gametophyte generation, a small (3) structure. 

called a (4), holds the (5) and the (6) cells. 

The fertilized egg produces leafy structures which bear (7) 

spores. The pteridophytes include the (8), the (9), 

and the (10). 



PROBLEM X. WHAT ARE SOME EXAMPLES OF 
SPERMATOPHYTES ? 

The spermatophytes (Gr. sperma, seed), or seed-bearing plants, 
include two groups : 

The gymnosperms (Gr. gymnos, naked), or naked-seed plants, 
are a small group related to the ferns on one side and the flowering 
plants' on the other. Two classes are found : the cycads, of which 
group the so-called tree ferns are examples, and the conifers or 
evergreens, as pines, spruces, firs, hemlocks, cypress, and others. 
There are only about 450 species of gymnosperms. The cycads 
are practically confined to the tropical regions. They have leaves 
much like the ferns and their stems are covered with scales. In 



206 



THE PLANT WORLD 



their life history as well as their appearance they show relationship 
to the ferns. They bear two kinds of reproductive bodies in 
conelike structures on separate plants. 

The conifers are the trees we call evergreens and most of them 
have needle-like leaves. The evergreens include the sequoias, the 
largest and oldest trees. The eggs and sperms are borne in pistil- 
late or staminate cones. Seeds are produced in the scales of the 



1 \ ■ fO 


| 1 


Ir, 




1 >fi 








■ag*^-— * **S£«^ 


: FAg^s-^r^r- 


|»JkBB9 1^1 


^ a 


"m-^ 




i:\ ■■" 










i 


9& mm 



Brooklyn Botanic Gardens, Brooklyn, N. Y. 
What are the characteristics of a cycad ? 

pistillate cones, and when the cone dies, the seeds are released by 
the curling backwards of the dry scales or sporophylls. 

The angiosperms (Gr. angeion, case or vessel), or true flowering 
plants, of which we already know something, are a very large 
group, including all of our common grasses and grains, and all 
trees, shrubs, and plants that bear flowers. There are more than 
240,000 known species. They are grouped in two great classes, 
the monocotyledons and the dicotyledons. 



WHAT ARE SOME EXAMPLES OF SPERMATOPHYTES ? 207 

If we summarize the facts we already know about flowering 
plants, they are briefly these : Seeds, which are formed in the 
fruits as the result of pollination and later fertilization, give rise 
under favorable conditions to young seedlings. The conditions 
which waken the embryo within the seed to activity and growth 
are favorable conditions of moisture, temperature, air, and food 
materials. We have learned that under favorable conditions the 
young plant grows into an adult and in course of time produces 
flowers. The flower is really a modified branch which contains 
the male and female gametophytes of the flowering plant. The 
female gametophyte is contained within the ovary of the flower 
and is called the ovule. The male gametophytes are the pollen 
grains which contain the sperm cells. 

Botanists have shown that in the flowering plants or spermato- 
phytes there exists an alternation of generations, as in the mosses 
and ferns. The pollen grain is believed to be a spore, which 
develops into the male gametophyte (the pollen tube), while the 
embryo sac in the ovary of the flower is another spore, within 
which is found the female gametophyte. Most of the life of the 
flowering plant is passed evidently in the asexual or sporophyte 
stage. 



SPERMATOPHYTA 



Gymnos^ermae — / \ An^ibspermae 

^fonoCot^ledoncteX L DicoWlecfoncte 






evergreen, plctnbs floral part?, 5k — parts ,41? wS$ 

The flowering plants are further divided into monocotyledons 
and dicotyledons. A brief description of a few of the most im- 
portant families of these plants is given. These particular ones 
were selected because they are likely to be seen by the average 
boy or girl who takes field excursions or hikes. The total number 
of known species of plants of these groups is more than 240,000. 



208 



THE PLANT WORLD 





," . 




>. 






• •' 


im^t '* 




*2&* 


^pdiatf^kv 


.*#' # s ;.''.»%.j s : . .;?i- 




;> 


S4ta^^3SSI 'T^M' m,-4B 


^M,' 


23it^N^ . jfiKjS Jf" : i '• 




, 


IMM1 




'^5'3£ 


w 

' f 

... o., ; .;.,.- ; , ,; V \: 


v; "" ' ■■ ^ 


SBmBRS^^v 


«N$'i 



Z/. IV. Brownell 
Jack-in-the-Pulpit (arum family) . 




L. W. Brownell 
Yellow Lady's Slipper (orchid family). 



Monocotyledons. The Grass 
Family. We are all familiar 
with the narrow parallel-veined 
leaf of the grasses. The stems 
are usually round and the 
flowers are borne in structures 
called spikelets. The flowers 
have three stamens and a 
single pistil, which produces 
one seed. The one-seeded fruit 
is called a grain. Examples of 
grasses are wheat, rye, timothy, 
wild grasses, sugar cane, and 
bamboo. The sedges, near 
relatives of the grasses, have un- 
jointed, triangular stems, while 
grass stems are always jointed. 

The Palm Family . The palm 
is known from other mono- 
cotyledons because it usually 
has a woody stem. There are 
about 1200 species of palms in 
the world. Though mostly 
inhabitants of the tropics, 
there are a few species found 
in the southern part of this 
country. 

The Lily Family . The mem- 
bers of this family are known 
to most of us. Hyacinths, 
tulips, lily-of- the- valley, as well 
as the tiger lily and other 
lilies, are members of this 
family. Several food plants, 
as asparagus and onions, be- 
long in this group. They have 
the typical liliaceous flower 



DICOTYLEDONS 



209 



with the parts in threes and 
with a brightly colored and 
often conspicuous corolla. 
They have bulbs, rootstalks, 
etc., which enable them to 
grow rapidly at the coming 
of a favorable season. The 
yucca, well known in our South- 
west, is one of this family. 

The Arum Family. The 
members of this family may be 
told by their peculiar flower 
cluster, a spikelike structure 
known as a spadix. In the 
Jack-in-the-pulpit this is sur- 
rounded by a large leaflike 
structure called the spathe. 
The calla lily and skunk cab- 
bage are our best-known ex- 
amples. 

The Orchid Family. These 
plants are noted for their 
beautiful flowers. In the 
tropics one member of this 
group is conspicuous because 
of its habit of living in trees 
as an air plant or epiphyte. A 
few orchids live in secluded 
places in our north temperate 
zone, but most have disap- 
peared because of overpicking. 
Never pick an orchid, if you 
are lucky enough to find one ; 
photograph it instead. 

Dicotyledons. Legume Fam- 
ily. This is one of the best- 
known and most easily recog- 




L. W. j 
Perennial peas (legume family) 


Srownell 




9w c - 


< 


ik - > 












Mm 


L^&IIS 



L. W. Brownetl 
Wild strawberry blossoms (rose family). 



210 



THE PLANT WORLD 



nized families of the dicoty- 
ledons. The legumes always 
have irregular flowers, as the 
sweet pea, and produce fruit 
which is a pod. Most of the 
legumes have compound leaves. 
Examples are : peas, beans, 
clover, lupines, and peanuts, 
while locusts and acacias are 
examples of trees. 

The Rose Family can be told 
by the flower in which the parts 
come out in fives, the sepals 
and petals making a cup from 
which the stamens spring. 
Roses, and the blossoms of 
strawberries, blackberries, rasp- 
berries, cherries, pears, and 
apples are examples. 
The Buttercup Family is a very large family, which bears solitary 
and conspicuous flowers in which the calyx and corolla are usually 
the same color. They have a large and indefinite number of 




L. W. Brownell 
Watercress (mustard family). 




W. Brownell 



The Globe flower is a member of the buttercup family. 



DICOTYLEDONS 



211 



stamens and pistils. Ex- 
amples are : buttercups, anem- 
ones, peony, tulip trees, mag- 
nolias, and many others. 

The Mustard Family has a 
peculiar flower of four petals 
and sepals distinct from each 
other and six stamens. Many 
of our most troublesome weeds 
belong to this family, as well 
as many garden vegetables, 
cabbage, turnips, radishes, and 
watercress. 

The Mint Family also has 
a characteristic flower. The 
corolla is like a tube and has 
two lips. The pistil has two 
carpels, but there are five sta- 
mens. The plants usually have 
a characteristic odor and square stems. Spearmint, lavender, and 
thyme are members of this family. 

The Willow Family is best known by the poplars and willows. 
These trees have the naked flowers in catkins with separate male 




L. W. BrowneJl 
Blossoms of the crack willow (willow family). 




L. W. Brownell 



Peppermint is a well-known member of the mint family. 



212 



THE PLANT WORLD 



and female flowers on different 
individuals. 

The Carrot Family can easily 
be recognized by the umbrella- 
shaped flower cluster. These 
plants are usually perennial 
herbs. The leaves are usually 
deeply indented. Examples are 
the carrot, fennel, and celery. 

The Heath Family can be 
recognized by the fact that its 
flowers have a five-parted 
corolla which is more or less 
united in a bell and most of 
the group have simple ever- 
green leaves. Laurel, blue- 
berries, wintergreen, heather, 
and rhododendrons are mem- 
bers of this group. 
The Composite Family is the largest group of the flowering plants, 
having over 13,000 species. The flowers are very small and grouped 




L. W. Brownell. 
Mountain laurel (heath family). 











"•-.•-""• -.™ - ~':-i*W -: 


i * 


v***** 1 *^ 




: .mm,. ■• a, • jammf?***- 


- «TOU -1*^ 






. ■■.-.■ 


4&S ■ ' .; 

sip* ■ ' 


*^<itik 


► JSW 1 aw* 


S «& ' ; v : ;-- **•-.. 


k ;' / ."• r ' 



Many fields are infested witn wua carrot (carrot family). 



L. IF. Brownell 



TEST ON FUNDAMENTAL CONCEPTS 



213 



in clusters known as compound 
heads. They produce numer- 
ous seeds. The group includes 
many of our weeds, such as 
ragweed, thistles, dandelions, 
daisies, and cockleburs, and 
many of our most beautiful 
garden flowers, as asters, sun- 
flowers, and chrysanthemums. 

Self-Testing Exercise 

The seed plants or (1) 

are divided into two great 

groups : the (2), those 

producing naked seeds, and the 

.(3), or (4) 

plants, in which the seed is 
usually inclosed in a (5). 





<r. *&m 






Wf - 
• 3 




4£ & 





L. W. Brovmell 
Daisies (composite family). 



Review Summary 

Test your knowledge of this unit by : (1) answering and rechecking the 
survey questions ; (2) performing all assigned exercises and in this case identi- 
fying a few common examples of plants ; (3) checking up with your teacher 
on the tests and doing over the parts you missed ; and (4) making an outline 
of the unit for your workbook. 



Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 2. 

I. Living things are classified (1) into groups, the members of which 
are like one another ; (2) into species, genus, order, class, and phylum ; 
(3) because they are then more convenient to study , (4) by placing 
them in groups which have certain characters in common ; (5) as species 
when they produce others like themselves and their offspring also pro- 
duce others like their ancestors. 

II. Bacteria (6) are small colorless animals ; (7) are found in all 
decaying things ; (8) reproduce rapidly by fission ; (9) may form spores 
and thus live under unfavorable conditions ; (10) are often parasites. 



214 THE PLANT WORLD 

III. Useful bacteria (11) cause decay of dead organic matter; 
(12) give flavors to foods ; (13) cause diseases ; (14) take nitrogen from 
the air ; (15) make fertilizers. 

IV. Bacteria (16) are killed by sterilization; (17) in milk cause it 
to sour ; (18) fix the nitrogen in the air ; (19) will grow readily in hot, 
dry places, provided they have food ; (20) may be killed by exposure 
to sunlight. 

V. Fungi (21), such as wheat rust, are responsible for great losses to 
crops each year ; (22) are able to make their own food ; (23) like molds, 
give flavor to cheese ; (24) are more useful than harmful ; (25) may be 
used as foods. 

VI. Yeast plants (26) are a kind of fungi ; (27) cause fermentation by 
means of their growth in fluids ; (28) cause bread to rise because they 
give off carbon dioxide gas in their growth; (29) produce carbon 
dioxide and alcohol in food substances; (30) reproduce by a process 
called budding. 

VII. Algae (31) are chlorophyll-bearing plants ; (32) cannot make car- 
bohydrate food; (33) have thread-like roots; (34) may reproduce by 
division of cells; (35) are one source of contamination of our drinking 
water. 

VIII. The main groups of the plant kingdom are (36) the angio- 
sperms, dicotyledons, and algae; (37) algae and fungi; (38) the 
mosses, lilies, palms, and trees; (39) the thallophytes, bryophytes, 
pteridophytes, and spermatophytes ; (40) phyla. 

IX. Alternation of generations (41) occurs when a plant gives rise to 
other plants just like itself; (42) is best seen in the algae; (43) in a 
plant takes place in two stages, one producing sexual cells, the other 
asexual spores ; (44) occur in the moss and fern, when the life history 
shows an alternating of the part of the plant bearing asexual spores 
with that part which bears sexual cells ; (45) occur in flowering 
plants, when the pollen grain and ovules represent the sexual genera- 
tion, while the seed and the plant that grows from it is the asexual 
generation. 

X. Spermatophytes (46) are seed-producing plants ; (47) are flower- 
ing plants only; (48) include both gymnosperms and angiosperms; 
(49) grow by means of asexual spores ; (50) include all of our common 
flowers, shrubs, and trees. 



TESTS 215 

Achievement Test 

1. How would you grow bacteria ? 

2. What is the favorite food of bacteria ? 

3. What are the factors necessary for bacteria to grow? 

4. In what ways are bacteria useful to the farmer? 

5. What are at least five parasitic fungi that do harm ? 

6. How would you prevent mold growth ? 

7. How can you explain the process of making bread ? 

8. What examples of all the four large groups of plants have you 
found in your environment ? 

9. Where would you find the following plants : red algae, pleuro- 
coccus, yeast, puffballs, pigeon- wheat moss, Christmas fern? 

10. How many flowers of the families of flowering plants mentioned 
in this unit have you been able to identify? 



Practical Problems 

1. Make a table showing all the ways in which bacteria affect your 
daily life for good or ill. 

2. Make similar tables for both molds and yeasts. 

3. Make a collection of your local flowering plants and classify 
them according to some simple key. 

4. Identify all the harmful plants in your locality. To do this get 
the use of a good manual on weeds or one of the state publications on 
weeds. The manual published by the University of Iowa is one of the 
best. 

Useful References 

Book of Knowledge. (Grolier Society.) 

Broadhurst, Home and Community Hygiene. (J. B. Lippincott Co. 

1925.) 
Conn, Bacteria, Yeasts. and Molds of the Home. (Ginn & Co. 1917.) 
Downing, Our Living World. (Longmans, Green & Co. 1924.) 
DeKruif, Microbe Hunters. (Harcourt, Brace & Co. 1926.) 
Kendall, Civilization and the Microbe. (Houghton, Mifflin. 1923.) 
Mathews, Book of Wild Flowers for Young People. (G. P. Putnam's 

Sons. 1923.) 
Parsons, How to Know the Wild Flowers. (Charles Scribner's Sons.) 




SURVEY QUESTIONS 

Can you distinguish between invertebrate and vertebrate animals? 
How many kinds of insects can you recognize? How many mollusks 
live in your locality ? How many kinds of fishes, reptiles, and birds can 
you identify ? How many mammals can you identify ? What is a fossil ? 



UNIT VIII 



HOW DO WE CLASSIFY ANIMALS? 

Preview. In the classification of animals, as well as of plants, 
there is one underlying principle which is used to show relationships. 
Living things which have similar structures or organs in similar 
parts of their bodies are almost certainly related to each other. 
Where structures are similar and are found in corresponding 
positions, they are said to be homologous. For example, the wing 
of a bat, the wing of a bird, the foreflipper of a dolphin, the fore- 
leg of a dog, and the arm of a man are homologous structures and 
show that these animals are, in a way, related to one another. On 

216 



ONE-CELLED ANIMALS 217 

the other hand, we often find that organs which do not have the 
same structure or origin are used for similar purposes. Such are 
the wings of a bird and the wings of a butterfly. Such structures 
are analogous. Analogy is likeness in function, regardless of origin. 

In our study of biology so far we have attempted to get some 
notion of the various factors which act upon and interact with 
living things. We have examined a number of forms of plants 
and have found all grades of complexity from the one-celled plant, 
Pleurococcus, to the complicated flowering plants of considerable 
size and with many organs. So in animal life the forms we study 
will show a constant change, and the change is toward greater 
complexity of structure and of function. A worm is simpler in 
structure than an insect, and shows by its sluggish actions that 
it is not so high in the scale of life as its more lively neighbor. 

We are probably aware of the fact that we are better equipped 
for the battle for life than lower animals, for we are thinking 
creatures and can change our surroundings if they are unfavorable, 
while the lower forms of animals are largely controlled by stimuli 
which come from without, such as temperature, moisture, light, 
and the presence or absence of food. 

There are a great many ways of arranging animals in groups. 
One way is to put all animals that have no backbones into a large 
group called the invertebrates as opposed to those which have a ver- 
tebral column, the vertebrates. 

PROBLEM I. WHAT ARE THE CHARACTERISTICS OF ONE- 
CELLED ANIMALS? 

Habitat of Protozoa. Protozoa, or one-celled animals, are found 
in water, seemingly never at any great depth. They appear to 
be attracted to the surface by light and by the supply of oxygen. 
Every fresh- water lake swarms with them; the ocean contains 
countless myriads of many different forms. 

Demonstration 1. To show a living amoeba. To obtain amoebas, 
crush some water plants and let the mass remain undisturbed for a week 
or so. Living animals will usually be found in the scum that forms. 
Mount a bit of the scum and observe it under a compound microscope. 
Describe the amoeba as to shape and size. 



218 



HOW DO WE CLASSIFY ANIMALS? 



Amoeba. The simplest of all animals is the amoeba, a tiny cell, 
which changes its shape as it moves about in the water. It has 
no organs of locomotion, nor of sensation, yet it is aware of the 
nearness of food. It has no mouth, but takes in food at any point 
in its body. It is able to change this food into living matter, 
- . ^ f° r it grows, and 

when it reaches a 
certain size, divides 
to form two amoebas. 
Several theories 
have been advanced 
to account for its 
locomotion: such as 
the flowing of the 
^4-lL|ood. Vacuole protoplasm, a rolling 

motion of the cell, 
and most recently 
the belief that the 
amoeba moves by a 
series of body con- 
tractions. 

Although but a 
single cell, the 
amoeba appears to 
be aware of the ex- 
istence of food when 
it is near at hand. 
Food may be taken 
into the body at any point, the semifluid protoplasm surrounds 
and takes in the bit of food, with a little water. Thus a food 
vacuole is formed. Digestion takes place in the vacuole by means 
of enzymes. As the food vacuole is circulated by the constant 
streaming of the protoplasm within the cell, the digested nutrients 
pass, by osmosis, from the vacuole into the protoplasm. Parts of 
the food material that cannot be used, such as the shells or outer 
coverings of tiny plants, are passed out of the food vacuole. Waste 
products, other than carbon dioxide, resulting from oxidation col- 



pseucCopocCium 



.ectoplasm. 
^^pJ^v. - - encCoplasm. 



-JLJ.Contndctile/ 
Vccotjeole^ 

nucleus 




State the use of each part that is labeled. 



THE PARAMECIUM 219 

lect in the contractile vacuole, which will burst and expel them. 
The cell absorbs oxygen from the air in the water by diffusion, 
and passes out carbon dioxide. Thus respiration takes place 
through every part of the outer covering of the cell. 

The amoeba reproduces by splitting into two cells, each of which 
resembles the parent cell, except that it is of smaller size. When 
these new cells become the size of the parent amoeba, they each 
divide. This is a kind of asexual reproduction. When conditions 
unfavorable for life come, the amoeba, like some one-celled plants, 
encysts itself within a membranous wall, forming a sporelike 
structure. Upon return of favorable conditions, the cover dis- 
appears and life begins again, as before. 

Laboratory Exercise. To learn something of the activities of a one- 
celled animal, Paramecium. Use material taken from the surface of 
a hay infusion made by placing a little hay in a beaker of water and 
letting the material stand for several weeks. Place a drop of the infu- 
sion on a slide, cover with a cover glass, and mount it under a com- 
pound microscope. 

Do the moving structures appear to have any definite shapes ? Do 
they move with any definite end forward? Do they collect in any 
locality? If so, what influences them to do this? 

Heat a needle and introduce it at one side of the cover glass. Is 
there any movement on the part of a Paramecium? 

Notice some of the animals grouped around small masses. Why do 
you suppose they are there? Notice other animals with reference to 
the position of air bubbles or to threads of Spirogyra to which they are 
attached. How do they lie with reference to the air bubble? What 
might the animal get from the air bubble, if it is to do work? How 
would a cell covered with a membrane take anything from an air 
bubble? What might it give in exchange? 

Drop a little fountain-pen ink on a slide containing Paramecia. 
Note the long structures (trichocysts) thrown out by the animal. 

Write a paragraph explaining how a Paramecium reacts to the stim- 
uli in its environment. Make drawings to illustrate your conclusion. 

The Paramecium. This one-celled animal is elliptical in outline, 
but somewhat flattened. The rounded (anterior) end of the 
body usually goes first. As the Paramecium pushes its way 
between dense substances in the water, the cell body is seen to 
change its shape as it squeezes through. 

The cell body is almost transparent, and consists of semi- 
fluid protoplasm bounded by a very delicate membrane, the pellicle, 



220 



HOW DO WE CLASSIFY ANIMALS? 




..dilicc 



Contractile 
va6uole> 



.rmcrDnucleus 
Tnacronueleus 



through which project numerous delicate threads of protoplasm 
called cilia (sil'i-d). 

Imbedded in the pellicle are many defensive structures called 
trichocysts (tnk'6-sist), which are shot out like darts when danger 

is near. These structures 
are composed of cytoplasm, 
are hollow, and secrete a 
poisonous substance. 

The locomotion of the 
Paramecium is caused by 
the movement of the cilia. 
The current of water 
caused by the cilia carries 
tiny particles of food into 
the oral groove on one side 
oral ^5h*?ve of the cell and into a 
funnel-like opening, the 
gullet. Once within the 
cell body, the particles of 
food materials are gathered 
within a small area called 
a food vacuole. Other 
vacuoles appear to be 
clear; these are spaces in 
which food has been di- 
gested. One or two larger 
contractile vacuoles may be 
found ; their purpose seems 
to be to pass off liquid 
waste material from the 
cell body. This is done 
by the pulsation of the 
vacuole, which ultimately bursts, passing the fluid waste to the 
outside. The cell wall breaks at regular intervals to discharge 
solid food waste. Since the cell membrane breaks at nearly 
the same place each time, the opening is called the anal spot. In 
a cell that has been stained, the nucleus is seen to be a double 



. — gullet 
:r|||"" yoocL vacuole** 



contractile 
vacixole^ 



The Paramecium. Which end goes first ? Where is 
the mouth ? How does food get inside the cell ? How- 
is it circulated ? 



THE PARAMECIUM 



221 



structure, consisting of one large and one small portion, called 
respectively the macronucleus and the micronucleus. 

Sometimes a Paramecium may be found in the act of dividing 
by the process known as fission. In this process the nucleus 
first elongates and breaks into 
two, and the halves go to op- 
posite ends of the cell. The 
cell elongates, a second gullet 
appears, and ultimately the 
cell breaks into two parts, each 
half provided with a nucleus 
and a gullet. This is a method 
of asexual reproduction. 

Frequently another type of 
reproduction may be observed. 





tile/ , 
vctcvole 



li^ronwcleus 
romxcleus 



lace -where 
torectk- 
occurs 



Conjugation in Paramecium. Explain 
how this takes place. 



Cell division in Paramecium. What is the proc- 
ess called? Describe exactly what happens. 



This is called conjugation, and somewhat resembles conjugation 
in the simple plants. Two cells of equal size attach themselves 
Together as shown in the small diagram. The cell membranes 
dissolve at the point of contact. Complicated changes take place 
in the nuclei of the two cells thus united. Finally fragments of the 



222 



HOW DO WE CLASSIFY ANIMALS? 



material forming the micronuclei of each cell pass over and unite 
with material forming the nuclei of the opposite cell. After this 
mutual exchange of nuclear material the cells separate. It is be- 
lieved that this stage of reproduction, as in the plants, is a sexual 
stage. 



Practical Exercise 1. Compare an amoeba and Paramecium as to size, 
shape, method of locomotion, method of taking in food, digesting food, excret- 
ing waste, and reproducing. 

The cell as a unit. In the daily life of a one-celled animal we 
find the single cell performing all the vital activities which we 
shall later find that the many-celled animal is able to perform. 
In the amoeba no definite parts of the cell appear to be set off to 
perform certain functions ; but any part of the cell can take in 
food, can absorb oxygen, can change the food into protoplasm, and 
excrete the waste material. The single cell is, in fact, an organism 
able to carry on the business of living as effectually as a very 
complex animal. 

Practical Exercise 2. Draw a cell and label all its parts. Give the use of 
each part. How do cells move about? What do we mean by conjugation? 
Why is the cell called a "unit of structure"? Why is a cell called an 
organism ? 



T^njjopocCcc 

Amoeba 



Infusoria 



VortiCelliX 




,wgrl&Vidc 



Plcc^rraootitcm 



The principal classes of Protozoa, examples of which we may have seen or read about, are — 

Class I. Rhizopoda (root-footed). Having no fixed form, with pseudopodia. Either naked 
as Amoeba or building limy (Foraminifera) or glasslike skeletons (Radiolaria) . 

Class II. Mastigoph'ora. They move by means of long whiplash threads of protoplasm, called 
flagella. Examples are Euglena and Monosiga. 

Class III. Infuso'ria (in infusions). Usually active ciliated Protozoa. Examples, Parame- 
cium, Vorticella. 

Class IV. Sporozo'a (spore animals). Parasitic and usually non-active. Example, Plas- 
modium malariae. 



PORIFERA 
Self-Testing Exercise 



223 



Protozoa are (1) composed of one (2). Examples 

are the amoeba, which (3) by changing its body form and 

the Paramecium, which moves by means of (4), tiny threads 

of (5) . These one-celled animals carry on all the (6) 

of higher animals, including (7) . 



PROBLEM II. WHAT ARE THE CHARACTERISTICS OF SOME 
SIMPLER INVERTEBRATES? 

Porifera (Lat. porus, pore ; ferre, bear) or sponges. The body 
of a sponge contains many pores through which water bearing food 
particles enters. They are classified according to the skeletons 
they possess into limy, glasslike, and horny fiber sponges. The 
last named are the sponges of commerce. Most sponges live in 
salt water ; they are never free swimming. There are about 2500 
known species. 



Calcccrecc 




Demispongia 



wantux 




Venuss- flave: 



bath. Sponge 



The following is the classification of Porifera : — 

Class I. Calca'rea, having limy spicules in the body. The Grantia seen along our northeastern 
coast is an example. 

Class II. Hexactinel'lida. Sponges having glasslike spicules, arranged on three axes. Exam- 
ple, Venus's flower basket. 

Class III. Demospon'giae. Sponges with glasslike spicules, not arranged on three axes, or 
with skeleton of horny fiber, the latter type represented by the bath sponge. 

The structure of a sponge. The simplest kind of sponge is hi 
the shape of an urn, attached at the lower end. Cut lengthwise, 
such an animal is seen to be hollow, its body wall pierced with 
many tiny pores or holes. These pores open into a central cavity, 
which in turn opens by a large hole, called the osculum (os'ku-lwm) 
or mouth, into the surrounding water. 



224 



HOW DO WE CLASSIFY ANIMALS? 




A microscopic examination shows the pores of the sponge to be 
lined on the inside with cells having collars of living matter sur- 
rounding a single long cilium called 
— mo«tk. flagellum (fla-jeTum). The flagella, 
.ectoccerm lashing in one direction, set up a cur- 
rent of water, bearing food particles, 
---fiatfelicc toward the large inner cavity where 
they are digested. The digested food 
w<t ** then passes by osmosis to the other 
cells of the body. From some of the 
H°St rrent cells in the jelly-like middle layer of 
the body lime is secreted to form the 
spicules, and the reproductive cells, 
Longitudinal section of a simple eggs, and sperms occur. The spicules 

sponge. How does this animal get -. , , , , , » . , 

its food? form the skeleton ol the sponge. 

Practical Exercise 3. Make a diagram of a simple sponge showing how food 
is taken in and waste given out from the body. How does a sponge breathe ? 

Coelenterates. The Coe- 
lenterates are a large group 
of animals, practically all of -™ 

which are found in salt 
water. They include the 
beautiful sea anemones, 
jellyfish, and corals. outer layers 

The Hydra. This little itmer ^"jgi. 
creature is shaped like a cc^ty^. 
hollow cylinder with a circle 
of arms or tentacles at the vva. 
free end. It is found at- 
tached to dead leaves, sticks, 
stones, or water weeds in 
fresh-water ponds. When 
disturbed, it contracts into 
a tiny whitish ball, a little f 00 ^ — 

larger than the head Of a Longitudinal section of Hydra. How does food 

. m, , /. . i get into the body ? How many layers of cells are 

pin. The outer layer of the found here? 




COELENTERATA 



225 



animal serves for protection as well as movement and sensation, 
certain cells being fitted for each of those different purposes. 

The tentacles are provided with thousands of minute darts or 
stinging cells, by means of which prey is killed. The tentacles 
then reach out like arms, grasp the food, bend over with it, and 
pull it toward the mouth. Certain cells lining the hollow digestive 
cavity pour out a fluid 
which digests the food. 
Other cells with long 
cilia circulate the food, 
while still other cells 
lining the cavity put 
out pseudopodia, which 
surround and take in 
the food particles. 
The outer layer of the 
animal does not digest 
the food, but receives 
some of it already di- 
gested from the inner 
layer. Oxygen is 
passed through the 
body wall, for there are 
no special organs for 
respiration. 

Reproduction. The 
Hydra reproduces asex- 
ually by budding, as is seen in the diagram. The bud appears on 
the body as a little knob, the body cavity extending into it. After 
a short time (usually a few days) the young hydra separates from 
the old one and begins life alone. This is asexual reproduction. 

The Hydra also reproduces by sex cells. The sperms develop in 
little groups near the free end of the animal, and the egg cells de- 
velop near the base. The sperms, when ripe, are set free in the 
water ; one of them unites with an egg, which is usually still at- 
tached to the body of the Hydra, and development begins which 
results in the growth of a new hydra. 




Colony of Obelia. 
A jellyfish. 



Amer. Mus. of Nat,. Hist. 



Why are the Obelia and jellyfish classified as coelenter- 
ates ? In what way are they similar ? In what ways are 
they unlike each other ? 



226 



HOW DO WE CLASSIFY ANIMALS? 



Practical Exercise 4. Study the diagram on page 224 and construct a cross 
section of the animal. Label all parts shown. 



HydCro*p<x 

Ofoelia v 




sea ai?$£mon<2, 

m " 



|coelenterata| 

Sc^pVzo^ocx / > Ctenophora 





#.,; 



jellyfish. 




comb jelly 



Class I. Hydrozo'a. Simple animals as hydra, or colonial in habit as the hydroids. They 
produce new individuals by budding, and the eggs and sperms are usually produced in a free- 
swimming jellyfish, which buds off from the original colony. This is an example of alterna- 
tion of generations. Examples : Hydra and Obe'lia. 

Class II. Scyphozo'a. Marine jellyfish, mostly of large size. Example, Aurelia. 

Class III. Anthozo'a. Hydralike animals, usually attached, with many tentacles, disposed 
in circlets in multiples of five. They may be single or colonial. The sea anemones and 
corals are the best-known examples. 

Class IV. Ctenophora, or sea walnuts, well known along our eastern coast, are sometimes 
given as a separate phylum and sometimes as a class of the coelenterates. 

Jellyfish. At first sight you would not say a jellyfish was re- 
lated to the Hydra, but we find that a part of the life of the 
jellyfish is passed as a colony of hydralike animals which give 
rise to free-swimming jellyfish as the sexual stage of their life 
history. This alternation of an asexual generation with that 
of a sexual generation, which produces the eggs and sperm 
cells, is seen in many plants and is best shown in this group of 
animals. 

Echinoderms. 1 These are spiny-skinned animals which live in 
salt water. They show radial symmetry. There are about 4500 
named species. 

The starfish. By far the most important enemy of the oyster 
and other salt-water mollusks 2 is the starfish. The common 
starfish, as the name indicates, is shaped like a five-pointed star. 
A skeleton of lime which is made up of thousands of tiny plates. 



1 Echinoderm : (e-kl'no-durm). 

2 Mollusk : popularly called shellfish. 



Has soft body protected by shell. 



ECHINODERMS 



227 



gives shape to the body and arms. Slow movement is effected 
by means of tiny suckers, called tube feet. The mouth is on the 
undersurface of the animal, and, when feeding, the stomach is 
protruded and wrapped around its prey. The body covering of 
the starfish, as well as that of the sea urchin and others of this 
group, is spiny ; hence the name echinoderm, which means spiny- 
skinned, is given to the group. 

Starfish are enormously destructive of young clams and oysters, 
as is shown by the evidence, collected by Professor A. D. Mead 
of Brown University. A single starfish was confined in an 
aquarium with fifty-six young clams. The largest clam was 
about the length of one arm of the starfish, the smallest about 
ten millimeters in length. In six days every clam in the aquarium 
was devoured. 

In order to capture and kill mollusks, the starfish wraps itself 
around the valves of the shell and actually pulls them apart by 
means of its tube feet, some of which are attached to one valve 
and some to the other of its victim. The mollusk can withstand 



AsteroicCea 



-.OphiuroicCea 

/ -brittle 




Ifchmoidea-' ttolothuroidea x Crir2oi<£ea 





urchi 



c c~c. - 



fioe** 



Sect feather 



Class I. Asteroi'dea, or starfishes. 

Class II. Ophiuroi'dea, the brittle stars or snake stars. 
Class III. Echinoi'dea, or sea urchins. 
Class IV. Holothuroi'dea, including the sea cucumbers. 

Class V. Crinoi'dea, or stonelike, deep-sea forms, now almost extinct; sea lilies and 
feathers. 



a strong pull, but not a long one, and so it eventually gives 
way. Once the soft part of the mollusk is exposed, the stomach 



228 



HOW DO WE CLASSIFY ANIMALS? 



of the starfish envelops it and covers it with the secretions of di- 
gestive glands, and it is rapidly digested and changed to a fluid. 

Hundreds of thousands of dollars' damage is done annually to 
the oysters in Connecticut alone by the ravages of starfish. 

Practical Exercise 5. What echinoderms, if any, exist in your community? 
What would you consider the chief characteristics of the echinoderms ? 

Platyhelminthes (Gr. platys, flat; helminthos, worm), or flat- 
worms. These are usually small, ribbon- or leaf-like, and flat. 
They live in water. Most flatworms are parasitic. The most 
commonly known ones are the tapeworm and the liver fluke. 
There are about 5000 known species. 



PLATYhELMINTHK 1 



Turbelloria.^ IfematocCa 




"Hon •.tpsCd cxsitio 



flxzkG, 



Cestoda 

\n 'ft 



Nemathelminthes (Gr. nematos, a thread), or roundworms. 
These three-layered, elongated threadlike animals are often par- 
asitic. Vinegar eels, the horsehair worm, the pork worm or trichina, j 
and the dread hookworm are examples. About 15,000 species are 
known. Examples of these worms will be discussed later in the unit 
''How Does Man Control His Environment for Health?" 



HCMATHELMINTHES 



Tsf^atooCa—/ AcantbocepWkr N Ckaetdghaika 




trichina* 



^«7^he<*i -*&rm. 




a.wo*f itf&rtiv 



THE EARTHWORM 



229 



Annulata (Lat. annulus, a ring). The segmented worms are 
long, jointed creatures composed of body rings or segments. The 
digestive tract is a tube within a tubelike body. They have no 
jointed appendages. There are about 4000 known species. 



Hirirdinecc 




sccnduwovytx 



Class I. Chaetop'oda. Many bristles along the sides of the body, 

worm or sandworm. 
Class II. Hirudin'ea. Without bristles and having suckers at both ends of the body 

amples are the leeches or bloodsuckers. 



leech 

Examples are the earth- 
Ex- 



Laboratory Exercise. Study of a living earthworm. Put several 
earthworms in shallow tin trays with moist blotting paper in bot- 
tom. Have paper wet at one end of tray and dry at the other. At 
which end of the tray do the worms gather? Wet the paper uni- 
formly and then cover one half of the tray with an opaque object. 
What happens to the worms? How do earthworms react to light 
and presence of moisture? 

Count the number of rings (segments) in your worm and compare 
with the estimates of others in the class. What conclusions do you 
draw? 

Watch a worm move. Describe exactly what happens. 

Notice the little swelling located about the thirty-first segment 
from the anterior tip. This is the clitellum and forms a bag in 
which the eggs are placed when laid. Rub the upper and lower sur- 
face of the worms with your fingers. Any differences ? Account for 
this. 

Find the mouth and posterior opening of the food tube. Can you 
find any other structures or openings ? 

Make a diagram of the first forty and the last five segments of the 
earthworm. 



The earthworm. The common earthworm is familiar to most 
of us. It has an elongated body made up of segments or rings. It 
is sensitive to food, to odors, to heat, to light, and to other 
stimuli. Four rows of tiny, movable bristles called setae are 
found on all the segments except the first three and the last. 
Locomotion is accomplished by the thrusting forward of the 

H. BIO — 16 



230 



HOW DO WE CLASSIFY ANIMALS? 



anterior end ; the setae there are anchored, then a wave of muscular 
contraction passes down the body, shortening the body by drawing 
up the posterior end. 

How the earthworm digs holes. The earthworm is not provided 
with hard jaws or teeth. Behind the mouth opening is a part of 
the food tube called the pharynx. It acts as a suction pump and 

draws particles of the soil into 
the food tube. Organic matter 
in the soil is used as food and 
the unused soil is passed out 
of the body and deposited on 
the surface of the ground, in 
the form of little piles called 
worm casts. Charles Darwin 
calculated that fifty-three 
thousand worms may be found 
in an acre of ground and that 
ten to fourteen tons of soil 
might pass through their bodies 
in a single year. 

Life processes of the earth- 
worm. The digestive tract of 
the earthworm is an almost 
straight tube inside of another 
tube. The latter is divided 
by partitions which mark the 
boundary of each segment. 
The outer cavity is known as 
the body cavity, and the inner 
cavity as the digestive tube. 
Food is digested within the 
food tube, passed through the walls of this tube by means of 
osmosis, and is absorbed by the blood which carries it to various 
parts of the body. The earthworm has no gills or lungs. The 
moist skin acts as an organ of respiration, taking in oxygen and 
giving off carbon dioxide. The nervous system is on the ventral 
side of the body but forms a ring around the food tube in the 



— — upper lip 

brain 

—-pharynx 
— nerve cord 

Tieart 

-testis* 

14 ovary 

crop 

T — &5yxr* 

-cforsal artery 
- intestine, 



A longitudinal section through an earthworm. 
In what segments are the hearts, the crop, the 
gizzard, the brain, the reproductive organs ? 




REPRODUCTION 



231 



anterior end of the body with a tiny brain just above the pharynx 
in the third anterior body segment. 

Reproduction. The earthworm has both male and female sex 
cells present in its body and hence is said to be hermaphroditic 
(her-mafro-dlt'ik). In order to have the eggs fertilized when 
they are laid a mutual exchange of sperm cells takes place between 
two worms, the sperms being placed in four little sacs on the under 
side of each worm. 
Later a swollen 
area called the cli- 
tellum (about one 
third the distance 
from the anterior 
end) forms a girdle 
which, as it passes 
toward the anterior 
end of the earth- 
worm, receives 
from body open- 
ings the eggs, the 
sperms received 
from the other 
earthworm, and a 
nutritive fluid in 
which the eggs live. 
The fertilized eggs 
are then left to 
hatch. The bags or cocoons may be found in manure heaps or 
under stones, in May or June. 

Practical Exercise 6. What worms are found in your locality ? Are there 
any useful ones? Any harmful ones? What is the difference between a 
worm and a caterpillar? 

Self-Testing Exercise 

Check the true statements in your workbook. 

T. F.- 1. Invertebrates have a backbone and an internal skeleton. 

T. F. 2. Protozoa are single-celled animals. 

T. F. 3. Sponges live only in the ocean. 








^®, sperms 

eggs are fertilijed,^ 

JN^S /"embryos 

^— J ^~\_ Capsule 



A secretion, given off by the clitellum of the earthworm, hardens, 
forming a cocoon or girdle which surrounds the body. What is 
the use of this girdle ? 



232 



HOW DO WE CLASSIFY ANIMALS? 



T. F. 4. Examples of coelenterates are sea anemones and starfish. 

T. F. 5. The Platyhelminthes are the roundworms. 

T. F. 6. An example of an annulata is an earthworm. 

T. F. 7. The earthworm has a digestive tract inside the body cavity 

T. F. 8. Starfish are echinoderms. 

T. F. 9. The Xemathelminthes are the roundworms. 



PROBLEM HI. WHAT ARE THE CHARACTERISTICS OF THE 
ARTHROPODS? 

Arthropoda (Gr. arihros, joint ; pous, foot). All animals which 
are jointed, have limy or chitinous exoskeletons, and jointed 
appendages belong to this phylum, Arthropoda. They live in 
water, or on land, or in the air. Most of them undergo a meta- 
morphosis. There are about 500,000 known species, more than all 
the rest of the animal kingdom put together. These animals are 
similar to the annelids or worms in that their bodies are composed 
of a number of segments. 



OnychcfphoTra 

peripetias 



Arachxiida 

Spider- 




CrustcrCecx 



Inseotcc 



: }*lVriapoc£ac 



<M*^cct> 




c£ig<ger* N/ctS"p 



CentipecCe 



Class I. Onychophora. These are simple wormlike animals. They live on land. 

Class II. Myriapoda (thousand legs'). They have long bodies with many segments and many 
paired jointed appendages. Centipedes and millepedes are examples. 

Class III. Crustacea. Thev live mostlv in the water and breathe by means of gills. lne 
head and thorax are fused 'into a hard covering. They have a " crusty " exoskeleton, strength- 
ened with lime. Examples : crabs and lobsters. . 

Class IV. Insecta. The largest of all classes of animals (over 450,000 species). Body 
segmented ; three regions : head, thorax, and abdomen. Three pairs of jointed legs. 
Usually compound eves. Breathe through tracheae or air tubes. 

Class V. Arachnida (a-rak'nl-da) . This group has no antennae, four pairs of legs, and a pair 
of claw-like appendages on each side of the mouth. Head and thorax combined as in 
Crustacea. The spiders, "daddy-long-legs," scorpions, mites, and ticks are in this class. 



THE CRAYFISH 



233 



The crayfish. Those animals having a limy exoskeleton, living 
in the water, and breathing by means of gills are called crustaceans. 
The crayfish is one of the best known representatives of the 
crustaceans. The body is covered with a hard skeleton, called 
exoskeleton, composed largely of lime. This forms an unjointed, 
shieldlike structure, the carapace, over 
the anterior part of the body, the ab- 
domen being segmented and movable. 
The coloring of the shell usually re- 
sembles that of its natural surroundings 
and therefore serves as a protection to 
the animal. 

Crayfishes dart backwards through the 
water with great rapidity, or they move 
forward by crawling on the bottom. 
They have five pairs of walking legs at- 
tached to the under side of the head-thorax 
region. These legs are jointed, and the 
first three pairs bear pincers. The large 
pincher claws or chelipeds (ke'li-ped) are 
used for food-catching and for defense as 
well as for locomotion. 

Under the abdomen, one pair on each 
segment except the last, are found jointed 
appendages, made up of three parts 
called swimmer ets. The last pair, together 
with the last segment of the abdomen, 
form a powerful tail used in swimming. 

How the crayfish gets in touch with its 
surroundings. Two pairs of " feelers/' the longer pair called the 
antennae, the shorter forked pair, the antennules (little antennae), 
are on the front of the head. The longer feelers appear to be 
used as organs of touch and smell. The smaller antennules hold 
at their bases little sacs called balancing organs. 

Just- above the antennules, projecting on short, movable stalks, 
are the compound eyes. These eyes are made up of many small 
structures each of which is a very simple eye. Such an eye 




State how the appendages are 
used by the crayfish. 1—5 are 
appendages found in the head 
region; 6-13, on the thorax; 
and M-19 on the abdomen. 



234 



HOW DO WE CLASSIFY ANIMALS? 



probably does not have very distinct vision. A crayfish, however, 
easily distinguishes moving objects and prefers darkness to light, 
as has been proved by experiment. 

Food-getting. The food of the crayfish is obtained with the aid 
of the pincer claws and shoved toward the mouth. It is pushed 
on by three pairs of small appendages called foot jaws or maxil- 
lipeds, and to some degree by two smaller paired maxillae just 
under the maxillipeds. Ultimately the food reaches the true 
jaws, or mandibles, and, after being ground between them, is 
passed down the gullet into the stomach. 

Digestion. Food which has not been ground up previously into 
pieces small enough for the purpose of digestion is still further 
masticated by means of three strong projections or teeth called 
the gastric mill, one placed on the mid-line and two on the side 
walls of the stomach. 

e ^ -brain L^^J 1 ^*? 

"^t ornac tt" ! r heccrt aorta intestine 




A crayfish, cut lengthwise to show the principal organs. 

The stomach is divided into two parts. The entrance to the 
posterior part is lined with tiny projections which make it act 
as a strainer for the food passing through. Thus the larger 
particles of food are kept in the anterior end of the stomach. 
Opening into the posterior end of the stomach are two large 
digestive glands, whose juices further prepare the food for absorp- 
tion by the walls of the stomach and intestine. Once in the blood, 



THE CRAYFISH 235 

the fluid food is circulated through the body directly to the tissues 
which need it. 

The gills. The plume-like gills are outside of the body, but are 
kept moist by being well protected by the overhanging carapace. 
The blood of the crayfish passes by a series of veins into the long 
axis of the gill, where the blood vessels divide into very minute 
tubes, the walls of which are extremely delicate. Oxygen, dis- 
solved in the water, passes into the blood by osmosis, during which 
process the blood loses some carbon dioxide. 

Circulation. The circulation of blood takes place in a system 
of thin- walled open vessels which allow the blood to come in direct 
contact with the tissues. The heart lies on the dorsal side of the 
body, inclosed in a delicate bag (see diagram). 

Excretion of wastes. On the basal joint of the antennae are 
found two projections, in the center of which are tiny holes. These 
are the openings of the green glands, organs which eliminate the 
nitrogenous waste from the blood, corresponding to the human 
kidneys. 

Practical Exercise 7. Study the diagram on page 234 and make a diagram 
of a cross section through a crayfish in the region of the walking legs. Ex- 
plain how a crayfish might become aware of the presence of food. How might 
it catch living prey? 

Nervous system. The internal nervous system of a crayfish 
consists of a series of collections of nerve cells called ganglia 
(gan' gli a), connected by means of a nerve cord. Posterior to 
the gullet, this chain of ganglia is found on the ventral side of 
the body. At the anterior end it encircles the gullet and forms a 
brain in the head region. From each of the ganglia, nerves pass 
off to the sense organs and into the muscles of the body. These 
nerve fibers are of two sorts, those bearing messages from the 
outside of the body to the central nervous system (these messages 
result in sensations), and those which take outgoing messages 
from the central nervous system, which result in muscular 
movements. 

Life history. The sexes in the crayfish are distinct. The eggs 
as they pass to the outside of the body of the female are fertilized 
by the sperm cells. The eggs, which are provided with yolk 



236 



HOW DO WE CLASSIFY ANIMALS? 



or food material, are glued fast to the swimmerets of the female, 
where they develop. The young cling to the swimmerets for 
several weeks after hatching. 

North American lobster. In structure the lobster is almost 
the counterpart of its smaller cousin, the crayfish. It is highly 
sensitive to changes in temperature, and migrates from deep to 
shallow water, or vice versa, according to changes in the tempera- 
ture of the water. The food supply, which is more abundant 




L. W. Brownell 

A rock crab. Crabs differ mainly from crayfish in having the abdomen much reduced. 
Crabs molt, or change their shells, with great frequency when they are young, but 
rarely after they are fully grown. 

near the shore, also aids in determining the habitat of the lobster. 
As it is the color of the bottom and as it passes much of its time 
among the weed-covered rocks, it is able to catch living food, 
even active fishes falling prey to his formidable pincers. It 
moves around freely at night, usually remaining quiet during the 
day, especially when in shallow water. It eats some dead food 
and thus is a scavenger, as is the crayfish. 

Several other relatives of the crayfish are the crabs of various 
species, used for food, on our eastern and western coasts ; the 
shrimps and prawns, thin shelled and small ; the fiddler crab, well 
known to boys and girls of the eastern coast, and the sea-spiders. 



INSECT AND CRUSTACEANS 



237 



These last-named ones are deep sea crabs and, in some parts of the 
world, grow to an enormous size. 

Insects and Crustaceans. We have already discussed the 
characteristics of all insects and the distinguishing features of 
certain orders of 

insects in Unit III. 

- 

The bodies of all 
insects are divided 
into three distinct 
regions: head, 
thorax, and ab- 
domen. Insects 
have three pairs 
of legs, breathe 
through tracheae, 
usually have two 
pairs of wings, and 
undergo a com- 
plete or incom- 
plete metamor- 
phosis. They are 
found everywhere 
that life can exist. 
Insects differ 

structurally from crustaceans in having three regions in the body 
instead of two. The number of legs is always definite in the in- 
sects; in the crustaceans the number sometimes varies, but is 
always more than three pairs. The exoskeleton is composed 
wholly of chitin x in the insects, but it is sometimes strengthened 
with lime in the crustaceans. Both groups have compound eyes, 
but those of the Crustacea are stalked and movable. The other 
sense organs do not differ greatly. The most marked differences 
are physiological. The crustaceans take oxygen from the water 
by means of gills, while the insects are air-breathers, using for this 
purpose air tubes called tracheae. Both insects and crustaceans, 
because of their exoskeleton, must molt in order to grow. 

1 Chitin (ki'tin) : a horny substance forming the outer covering of insects. 




fall grown larvcr 



Life history of a moth. Why is the moth classified as an insect ? 
How does it differ from a crustacean? 



238 HOW DO WE CLASSIFY ANIMALS? 

There are a number of orders of insects, but examples of the 
following orders are the ones most commonly found. 

Order 1. Coleop'tera (sheath wings). Hard outer wings, forming 
cover for under wings. Biting mouth parts. Complete meta- 
morphosis. Examples : all beetles and fireflies, etc. 

Order 2. Dip'tera (two wings). Insects with two wings, a few 
with none. Mouth parts fitted for sucking or piercing. Com- 
plete metamorphosis. Examples : all flies, mosquitoes, gnats, etc. 
There are 40,000 described species and it is estimated that there 
are more than 300,000 as yet undescribed. 

Order 3. Ephemer'ida. Insects having complete metamorphosis 
and biting mouth parts. They have long setae which project 
from the end of the abdomen. The adult lives only a day or two, 
lays eggs, and dies. Examples : the mayflies. 

Order 4. Hemip'tera (half wings) . Sucking mouth parts. Incomplete 
metamorphosis. Two pairs of wings or none. Examples : 
chinch bugs and squash bugs. 

Order 5. Homop'tera (similar wings). Two pairs of wings alike, 
sucking mouth parts, incomplete metamorphosis. Examples : 
cicadas, plant lice, scale insects. 

Order 6. Hymenop'tera (membrane wings). Four membranous 
wings. Mouth parts fitted for biting and sucking. Often long 
ovipositor modified into sting. Complete metamorphosis. Ex- 
amples : bees, ants, and wasps, gall and ichneumon flies. 

Order 7. Lepidop'tera (scale wings). Four wings, covered with 
scales. Mouth parts long sucking tube. Complete metamor- 
phosis. Examples : Moths and butterflies. 

Order 8. Neurop'tera (veined wings). Four membranous wings 
with many veins. Biting mouth parts. Complete metamor- 
phosis. Examples : ant lions, dobson flies, etc. 

Order 9. Odon'ata. Complete and incomplete metamorphosis. 
Biting mouth parts. Adults are expert flyers, have large eyes, 
live mostly in water. Examples : dragon flies and damsel flies. 

Order 10. Orthop'tera (straight wings). Four wings, front pair 
straight and leathery. Biting mouth parts. Incomplete meta- 
morphosis. Examples : grasshoppers, crickets, and cockroaches. 

Order 11. Siphonap'tera (tube; wingless). Largely parasitic. 
Sucking mouth parts. Wingless. Complete metamorphosis. 
Examples : fleas. 

Order 12. Trichop'tera (hairy wings) have four hairy wings, rudi- 
mentary mouth parts, complete metamorphosis. Examples : caddis 



Arachnids (spiders) and myriapods. The body of a spider, like 
that of the crustaceans, has only two divisions, cephalothorax 
(head thorax) and abdomen. Spiders have four pairs of walking 
legs, usually four pairs of simple eyes, and breathe by means of 






SPIDERS AND MYRIAPODS 



239 




U. S. Bureau of Entomology 
Is a spider an insect ? Why ? 



lunglike sacs in the abdomen. 
They have no wings or com- 
pound eyes. The silk with 
which they spin their webs is 
secreted by means of glands in 
a liquid form. On exposure to 
air this fluid hardens and forms 
a very tough thread which is 
light and strong. 

We are all familiar with the 
harmless " thousand leggers " 
found under stones and logs. It- 
is a representative of the group 
of animals known as the mille- 
pedes. These animals have a 

rounded body divided into two regions, 
head and trunk, and have two pairs of 
legs on each body segment. They live 
in damp places and feed on decaying 
vegetable matter. They are entirely 
harmless. The centipedes are long 
flattened animals with one pair of legs 
on each segment. Both the millepedes 
and centipedes are representatives of 
the class Myriapoda. 

Practical Exercise 8. Make four diagrams 
to show the likenesses and differences between a 
crustacean, an insect, a myriapod, and a spider. 
Use books of reference for information. Use 
colors for different structures, as yellow for exo- 
skeletons, blue for nervous system, red for blood 
vessel or heart, etc. 

Practical Exercise 9. Name all the arthro- 
pods you have found living in your environ- 
ment. Which live in water? On land? In 
both habitats? 

Practical Exercise 10. Study the diagrams 
of the Arthropods. How many legs has the crab, 
the centipede, the insect, the spider? Study a 
real crab and centipede to see how they differ 
u. s. Bureau of Entomology from the insects. From the above study can you 
Why is a centipede an Arthropod ? make a working definition of an Arthropod ? 




240 



HOW DO WE CLASSIFY ANIMALS? 



Self-Testing Exercise 

Arthropods are animals which have (1) (2) and legs 

and have a hard (3) (4) made of either (5), 

(6), or both. There are four common (7) ; crus- 
taceans, which live mostly in (8) and breathe by means of 

(9) ; insects, a (10) group, which has the (11) 

divided into (12) parts, and has three (13) of jointed 

(14) ; the myriapods which have ......... (15) bodies with 

(16) pairs of (17) ; and the arachnida, spiders, with 

. . (18) pairs of legs and no ........ (19), and (20) 

pairs of simple eyes. The spiders spin (21) from silk which they 

(22) by means of glands. 

PROBLEM IV. WHAT ARE THE CHARACTERISTICS OF THE 

MOLLUSKS? 

Most mollusks have shells composed mostly of lime, either 
bivalve (two-valved), as the oyster, clam, mussel, and scallop, 
or univalve (with one valve), as the snail. Usually the univalve 
shell is spiral in form. Inside the shell, which is formed by a 
F . . delicate structure called 

the mantle, is found the 
soft, unsegmented body, 
from whence it gets the 
name mollusk (Latin mol- 
lis, soft). Other mollusks, 
for example the garden 
slug, have no shell what- 
ever, and one highly 
specialized form, the squid, 
has an internal shell. 

Pelecypods. Between 
the mantle and the body 
of the mollusk is a space, 
the mantle cavity, in which 
hang the platelike gills. 
By means of cilia on the 
mantle and gills, a con- 

A fresh-water mussel (clam) half buried in the mud. £ ..J 

Explain how it moves and how it gets its food. Slant Current 01 Water IS 



'ipKons- 



ouL 



^vfcrter 




MOLLUSKS 



241 




foot mouth. 

A gastropod (snail). Why is this a mollusk? 



maintained through the mantle cavity, bearing oxygen to the gills 
and carbon dioxide away from them. In most mollusks, this 
current of water passes into 
and out from the mantle 
cavity through muscular 
tubes called siphons. 

The food of clams or 
oysters consists of tiny 
organisms which are carried 
in the current of water to 
the mouth of the animal, this water current being maintained in 
part by the action of cilia on the palps or liplike flaps surround- 
ing the mouth. A single muscular foot enables the clam to move 
about slowly. 

Gastropods. Snails, whelks, slugs, and the like are called 
gastropods (stomach-footed) because the foot occupies so much 
space that most of the organs of the body, including the stomach, 
are covered by it. 

Cephalopods. Another class of mollusks are those known as 
cephalopods (sefa-16-podz). The name means head-footed. As 

__Ffelecxpoc£ct 



Ampkineura 




dhitcm, 

ScaphocCcc 




tu&ukxr^ shelled: 





ctccm: 

Cephalop^Gcr 



-s^uict 



Class i. Pelecyp'oda (hatchet-footed). Shells of two valves or parts. Clams, oysters, scallops, 

mussels, etc. 
Class II. Cephalop'oda (head-footed). Foot partly surrounds head and bears tentacles or 

grasping organs. Squid, octopus, cuttlefish, etc. 
Class III. Gastrop'oda (belly-footed). With or without shells, which are usually of one piece 

and coiled. Snail, whelk, slug. 
Class IV. Scaphoda. With a tapering tubular shell, with a spadelike foot for burrowing. 

Tooth shells. 
Class V. Amphineura. Simple marine mollusks. Protected by a shell of eight arched 

segments. Chiton. 



242 HOW DO WE CLASSIFY ANIMALS? 

the figure of the squid shows, the mouth is surrounded with a 
circle of tentacles. The shell is internal or lacking. 

To this group of animals belong also the octopus, or devilfish ; 
the paper nautilus ; and the pearly nautilus. 

Practical Exercise 11. From a study of the diagrams and of the text, make 
up a good definition of a mollusk. What mollusks are common in your 
environment ? 

Mollusca. These animals are soft-bodied animals, often pro- 
vided with a shell, which is secreted by a part of the body called 
the mantle. They usually have a single muscular foot on the 
ventral side. Over 60,000 species are known. There are five 
classes of mollusks, but only three classes are widely known. 

Self-Testing Exercise 

A mollusk is a (1) animal. It usually has a (2) 

which is (3) by the mantle. This (4) is either 

(5) as in the oyster, or ........ (6) as the snail. Most 

mollusks, living in the water, take in waiter through (7) tubes 

called (8). Common examples of mollusks are (9), 

(10), and (11). 

PROBLEM V. WHAT ARE THE CHARACTERISTICS OF FISHES? 

The animals we have studied thus far agree in having any skeleton 
they may possess on the outside of the body. They are called 
invertebrates. In higher animals, of which the fish is an example, 
the skeleton is inside the body. They are called vertebrates. While 
the exoskeleton of invertebrates is dead material secreted by the 
body cells the endoskeleton of vertebrates is made up of cartilage 
and bone, living material, capable of growth and repair. The 
skeleton of all Vertebrates has two main divisions, the axial skeleton, 
consisting of the skull and vertebral column and the appendicular 
skeleton, consisting of two pairs of limbs together with the girdles, 
the bones, by which the limbs are attached to the vertebral column. 
The vertebral column and skull protect the delicate spinal cord 
and brain. The limbs support the body and aid locomotion. 
Vertebrates are segmented but these segments have been highly 
modified to form the various organs. Vertebrate animals deserve 
more of our attention than other forms of life because man himself is 



THE BODY OF A FISH 



243 



a vertebrate. There are 37,000 known species of vertebrates. 
These species are divided into five groups or classes : Pisces, or 
fishes ; Amvhibia, or amphibians ; Reptilia, or reptiles ; Aves, 
or birds; Mammalia, or iTKnnials. 

skeleton../ \ / ^^^V_\ skeleton. 

htatb.4— ^O J ^ G^-feSS 

V J \ v -/-KidCtiey 

nerve ^V^-co ^/^ \ m.—^.-Jieorr'b 

cord ^- 11-^ V_l^ 

invertebrate/ ver-tebrette 

Cross section of an invertebrate and of a vertebrate. In what ways are they similar? 
In what ways do they differ ? 

Laboratory Exercise. Adaptations in a fish. How is the body of 
the fish fitted for life in the water? Mention three different adapta- 
tions for swimming. Watch the fish carefully and locate its organs 
of locomotion. How many single fins are there? How many paired 
fins? 

Try to discover what fins are used in forward motion, in turning, in 
moving backward. Is the body used in locomotion. How is each 
particular fin adapted or fitted to do its work? 

What structures do you find on the surface of the body ? How are 
these structures placed with reference to each other? Feel the body 
of the fish. What adaptation for protection exists here? Note the 
color both above and below. Remembering that many of the enemies 
of the fish are below him and some above, explain how the animal 
receives protection from its color. What are the principal adaptations 
for protection in the fish ? j 

Look at the living fish carefully and observe the movements of the 
mouth. What is the relation of the movement of the mouth to that of 
the operculum, the flap which covers the gills? Note position and 
color of the gills. What gives them this color? Put a few grains of 
carmine in the water in front- of the mouth of the fish. Trace the 
course of the carmine. Where does it come out ? What gas is in the 
water? How does the fish use this gas? How might this gas come in 
contact with the gills? Write a paragraph and illustrate with a 
diagram, showing how a fish breathes. 

The body. The long, spindle-shaped body, pointed at the 
anterior end, with its smooth surface, admirably adapts a fish 
for swimming. Mucus 1 secreting cells in the skin, and the position 

1 Mucus: a sticky slippery secretion found on the membranes lining various 
body cavities, as the nose or mouth. 



244 HOW DO WE CLASSIFY ANIMALS? 

of the scales, overlapping in a backward direction, are other 
adaptations for life in water. 

The paired fins are called pectoral and pelvic fins because they 
are attached to the bones forming thetiTuctoral and pelvic girdles. 
These fins are homologous to the foxelimbs and hindlimbs of 
higher animals. The dorsal, anal, and caudal fins are not paired. 

A fin is composed of a thin membrane or skin stiffened by long 
slender spines of bones or cartilage called rays. The caudal fin 
is light and strong, and, as powerful muscles are attached to it, 
can push against the water with sufficient force to move the body 
forward. The flattened, muscular body of the fish, tapering I 



^ostri^ 



,-firs-t dons-al fin 

,. second 
^« cCprs-ocl 

.Caudal fin 



i i. » *• jJ$rf// ' t'wi/ ,- second: 

lateral * m &/i ill /. trlt'fmr ^ ' ccons-ocl 

uJm ... ■-■ IK v^HbL f in. 



I mouth \V\^ -pelvic fin i — anal fin 

Name all the adaptations you can find in the body of this fish and show how each 
is an adaptation. 

toward the caudal fin, is moved from side to side with an undulating 
motion which results in the rapid forward movement of the fish. 
The caudal fin is the principal fin of locomotion. The paired fins 
are used for turning and balancing. 

The sense organs. The eyes, globular in shape, are on each 
side of the head. They are unprotected by eyelids, but their 
tough transparent outer covering and their position in the sides 
of the head afford some protection. A fish becomes aware of the 
presence of food by smelling it rather than by seeing it. The 
nostrils, small pits unconnected with the mouth cavity, contain 
organs for smelling. In the catfish, the barbels, or horns, receive 
sensations of feeling, smell, and taste. 



GILLS OF A FISH 



245 



Along each side of most fishes is a line of tiny pits, provided with 
sense organs and connected with the central nervous system. This 
area, called the lateral line, is believed to be sensitive to mechanical 
stimuli of certain sorts. The ear of the fish is under the skin and 
serves partly as a balancing organ. 

Breathing. A fish, when swimming quietly and when at rest, 
seems to be biting even if no food is present. Investigation shows 
us that under the broad, flat plate, or operculum (6^pur'ku-l#m), 
on each side of the head, lie two pairs of long, feathery structures, 
gills. The skeleton of the gill, or the gill arch, is composed of 



ondtair- 




filament 
illrakens 



Explain why a fish in an aquarium is continually opening and closing its mouth. 

several pieces of bone which are hinged in such a way as to give 
great flexibility. Covering the bony framework, and extending 
from it, are numerous delicate gill filaments. These delicate 
structures are guarded on the inner side by a series of teeth-like 
structures, the gill rakers. In each of these filaments are two 
blood vessels; one taking blood to the gilte, where it gives up its 
supply of carbon dioxide, the other vessel taking the blood with 
; its load of oxygen back over the body. A thin membrane sepa- 
rates the blood in the filament from the water bathing the gills. 
An exchange of gases through the walls of the gill filaments 
results in a loss of carbon dioxide and a gain of oxygen by the 
blood. 

f bio — '7 



246 



HOW DO WE CLASSIFY ANIMALS? 



Digestive system. The gullet leads directly into a baglike 
stomach. There are no salivary glands in the fishes. There is, 
however, a large liver, which appears to be used as a digestive 

gland. The liver contains 
a good deal of oil and there- 
fore is in some fishes, as the 
cod, of considerable eco- 
nomic importance. Many 
fishes have outgrowths like 
a series of pockets from the 
intestine. These structures, 
called the pyloric caeca (pi- 
lor'ik se'kd), are believed 
to secrete a digestive fluid. 
The intestine ends at thei 
vent, or anus, which is usu- 
ally located on the ventral 
side of the fish, immediately 
in front of the anal fin. 

Swim bladder. An organ 
of unusual significance, 
called the swim bladder, 
occupies the region just} 
dorsal to the food tube. 
The size of the swim bladder 
can be changed by contrac- 
tion or expansion of its 
walls. The fish uses this 
organ to make changes in 
position so that the water 
displaced will equal its own 
weight. In some fishes it is: 
used as a lung. 

Circulation of the blood. In fishes the heart is a muscular^ 
organ, with two connecting chambers : a thin-walled auricle, or 
receiving chamber, and a thick- walled, muscular ventricle from; 
which the blood is forced out. The blood is pumped from the; 




.filament 

^^...arterx 

^^ : --giW arch 






Explain, by careful study of the diagram, how 
the blood receives oxygen and how it gets rid of 
carbon dioxide in the gill. 



EGG-LAYING HABITS OF BONY FISHES 



247 



heart to the gills, where it loses carbon dioxide and receives oxygen ; 
it then passes on to other parts of the body, until it reaches very 
tiny tubes called capillaries. From the capillaries the blood 
returns, in veins of gradually increasing diameter, to the heart 
again. During its course around the body some of the blood 
passes through the kidneys and is there relieved of its nitrogenous 
waste. Circulation of blood in the fish is rather slow. Since the 
temperature of the blood is nearly that of the water in which the 
fish lives, fishes are called cold-blooded animals. 

Nervous system. As in all other vertebrate animals, the 
nervous system of the fish consists of the brain and spinal cord. 



hrai 




heart 

gall blacCcC^^si^E^^^ 

Diagram of a fish cut lengthwise to show the relative position of the internal organs. The 
veins, arteries, and all smaller organs a e omitted. Where would the gills be with reference 
to the heart? Why? The swim bladder is attached to the fool tube. What is the value 
of this ? 

Nerve cells located near the outside of the body send messages 
to the brain, where they are received as sensations. Cells of the 
central nervous system, in turn, send out messages which result 
in the movement of muscles. 

The egg-laying habits of the bony fishes (teleosteans) . The eggs 
of most bony fishes are laid in great numbers. The number varies 
from a few thousand in the trout to many hundreds of thousands 
in the shad and several millions in the cod. The time of spawning 
is usually spring or early summer. After the eggs are laid the 
male usually deposits milt, consisting of millions of sperm cells, 
in the water just over the eggs. The sperm cells move rapidly 
through the water to the egg cells, and unite with them, thus 
bringing about fertilization. Some fishes, as sticklebacks, sunfish, 



248 



HOW DO WE CLASSIFY ANIMALS? 



toadfish, etc., make nests, but usually the eggs are left to develop 
by themselves, sometimes attached to some submerged object, but 
more frequently free in the water. Some eggs which have a tiny 
oil drop are buoyed up to the surface, where the heat of the sun 








\ 



— yoik 



.recently* 

yzxtcbed -'larva 

1.5 mm. 





dgelopin£ 



<//Zs 




% 



sevens! \faotitbs dd 



U. S. Bureau of Fisheri 



The pigfish or hogfish is a bony fish. It is found from New York to Mexico. The eggs are 
laid in the early spring, and may hatch within 2 or 3 days. A recently hatched larva is about 
1.5 millimeters long. A young fish of several months is 26 or more millimeters long. 

aids development. Both eggs and developing fish are exposed to 
many dangers, and are eaten, not only by birds, fish of other 
species, and other water inhabitants, but also by their own 
relatives and even parents. Consequently very few of the eggs 
ever reach maturity. 



FISHES 



249 



Practical Exercise 12. Give a brief definition of a fish that will fit all fishes. 

Using the diagram on page 247, reconstruct a cross section passing through 
the heart. Use colors for the different organs. 

After watching a fish swim make a diagram to illustrate how a fish moves 
forward in the water. 

Fishes. All fishes live in the water. They usually secure 
oxygen by means of gills.- They move by means of appendages 
called fins. Four of these fins are paired and are homologous to 
the legs and arms of man. They all possess a vertebral column. 



'Zlasmohrancbi __ 



<3 



ctnoid_ 







PISH£S 




"Butterfly fisS* , _... 

.Dipnoccn 





Order 1. Elasmobranch. Fishes which have a soft skeleton made of cartilage, and exposed 
gill slits. Examples : sharks, skates, and rays. 

Order 2. Ganoid. Fishes which once were very numerous on the earth, but which are now 
almost extinct. They are protected by platelike scales. Examples : gars, sturgeon, and 
bowfin. 

Order 3. Teleostans, or Bony Fishes. They compose 95 per cent of all living fishes. In this 
group the skeleton is bony, the gills are protected by an operculum, and the eggs are numer- 
ous. Most of our common food fishes belong to this class. 

Order 4. Dipnoan, or Lung Fishes. This is a very small group. In many respects they are 
more like amphibians than fishes, the swim bladder being used as a lung. They live in 
tropical Africa, South America, and Australia, inhabiting the rivers and lakes there. 



Self-Testing Exercise 

Fishes have a (1) made up of irregular-shaped bones. 

This is called the (2) (3). In addition there is an 

exoskeleton which may take the form of (4) . The fish is 

adapted for life in the water by the (5) of its body, 

(6) glands in skin and (7) for breathing. The fish has a 

(8) (9), a (10) chambered heart and a well- 
defined nervous system consisting of a (11), (12) 

'. . (13), and (14) organs. Many (15) are laid 

but only a (16) reach maturity as the (17) are 

exposed to many (18) and are eaten by other (19) 

as well as other enemies. 



250 HOW DO WE CLASSIFY ANIMALS? 

PROBLEM VI. WHAT ARE THE CHARACTERISTICS OF 
AMPHIBIANS? 

Laboratory Exercise. Adaptations in a living frog. Examine the 
skin, note body shape, shape of head, etc., of a frog. What adapta- 
tions for its life in the water can you find ? 

Examine the appendages. How are they adapted for locomotion? 
Note their position in relation to the long axis of the body. What are 
the positions of the webbed toes, and of the legs, when at rest and when 
swimming or jumping. 

Compare the position of the eyes of the frog with those of a fish; 
with your own eyes. In which directions can a frog see? Note the 
eardrum just back of the eye. What evidence have you that a frog 
can hear? 

Watch a frog catch a fly or other prey and explain how it is done. 
Examine the mouth of a dead frog. Where is the tongue ? How is it 
attached ? How might it be used ? Does a frog have teeth ? How 
do you think it eats its food after catching it ? 

Look for movements of the throat, nose, and abdomen of a quiet 
frog. Does the frog open its mouth while breathing ? Can it breathe 
under water? Can you describe the process of breathing in a frog? 

Sense organs. The frog is well provided with sense organs. 
The eyes are large, globular, and placed on each side of the head. 
When the frog goes under water, a delicate fold, called the nictitating 
membrane (or third eyelid), is drawn over each eye. The vision 
of a frog is much keener than that of the fish. The external ear, 
tympanum (tmi'pd-mmi), is located just behind the eye on the 
side of the head. Frogs hear sounds and distinguish various 
calls of their own kind, as is proved by the fact that they recognize 
the warning notes of their mates when any one is approaching. 
The inner ear has to do with balancing the body as it does in fishes 
and other vertebrates. Touch is a well-developed sense. Frogs 
respond to changes in temperature under water, and go into a 
dormant state for the winter when the temperature of the air 
becomes colder than that of the water. Taste and smell are 
probably not strong sensations in a frog. 

Food-getting and digestion. The frog's mouth is large and can 
be opened very wide. Its sticky tongue is long and flexible. It 
is attached to the front of the floor of the mouth and can be 
thrown out with great rapidity to secure living prey. The mouth j 
leads into a short tube, the gullet, which widens into a long stomach. 



FROG 



251 



The stomach in turn leads into a narrow, much-coiled small in- 
testine, which widens to form the large intestine, the last part of 
which is the cloaca (Latin, sewer). The kidneys, urinary bladder, 
and reproductive organs {ova- N 

ries or testes) open into the 
large intestine. Several glands, 
the gastric glands, the liver, and 
the pancreas, produce digestive 
fluids. These digestive fluids 
by means of enzymes change 
insoluble food materials into a 
soluble form which may be ab- 
sorbed and become part of the 
blood. 

Breathing. The frog takes 
air into its mouth by lowering 
the floor of the mouth and 
drawing air in through the two 
nostril holes. Then the little 
valve-like flaps over the holes 
are closed, the floor of the 
mouth is raised, and the frog 
forces the air down into the 
baglike lungs. When the nos- 
tril flaps are lifted the air is forced back to the mouth by the 
pressure of the body wall and the contraction of the lungs. 
Then the mouth floor is raised and the air is forced to the 
exterior. The lungs contain air spaces surrounded by walls filled 
with small blood vessels, by means of which oxygen is taken up 
and carbon dioxide is given off. The skin also is provided with 
many tiny blood vessels which absorb oxygen and give off carbon 
dioxide. 




Explain how the frog captures its food. 



Practical Exercise 13. How does a frog breathe during his winter sleep at 
the bottom of a pond? 

Circulation. The frog has a well-developed heart, composed 
of a thick-walled muscular ventricle and two thin-walled auricles. 



252 



HOW DO WE CLASSIFY ANIMALS? 



heart, 
lung., 
gall bladd 
pancreas 

Spl<sen. I 



cloocca».._ :! ^..j 



_ —gullet. 



stomach. 



kidney 



HacCden 



The heart pumps the blood through a system of closed tubes to 
all parts of the body. Oxidation must take place in the cells of the 
body wherever work is done. Food in the blood is taken to the 

muscle cells or other 
cells of the body and 
there oxidized. The 
products of oxidation, 
chiefly carbon dioxide, 
and any other organic 
wastes given off from 
the tissues must be 
eliminated from the 
body. As we know, the 
carbon dioxide passes 
off through the lungs 
and to some extent 
through the skin of the 
frog, while the nitrog- 
enous wastes are elimi- 
nated by the kidneys. 

Nervous system. 
The frog has a brain 
and spinal cord and in general its central nervous system resembles 
that of man. 

Reproduction and life history. The eggs of the common frog 
are laid in shallow water in the early spring. Masses of several 
hundred, which may be found attached to twigs or other supports 
under water, are deposited at a single laying. Immediately 
before leaving the body of the female they receive a protective 
coating of jellylike material, which swells up after the eggs reach 
the water. The upper side of the egg is dark, the light-colored side 
being weighted down with a supply of yolk (food). The eggs are 
fertilized in the water by sperms which are discharged about the 
same time as the eggs. The fertilized egg soon divides into many 
cells and in a week or ten days, if the weather is warm, it devel- 
ops into a tiny oblong body with a wide tail and indistinct head, 
which wriggles itself free of the inclosing jelly. This form is known 




A dissected frog. Seen from the under side. What 
systems are represented in this figure? What parts are 
left out of the drawing or are not labeled? 



REPRODUCTION AND LIFE HISTORY 



253 



as a " tadpole" or "polliwog." At first it is attached to some 
water weed by means of a suckerlike projection ; but in one or 
two weeks' time, depending upon temperature, it frees itself 
and becomes a free-swimming tadpole. A mouth is formed at 
the suckerlike projection, and the tadpole begins to feed upon 
algae and other tiny water plants. At this time, gills are present 
on the outside of the body. Later, these gills are replaced by 
others which grow out under the fold of the skin. Water reaches 
the gills through the mouth and passes out through a hole on the 
left side of the body. As the tadpole grows larger, legs appear. 
The hind legs grow out first. At the same time the tail becomes 
shorter and shorter. Shortly after the legs appear, the gills are 
absorbed, and lungs take their place. At this time the young 
animal may be seen coming to the surface of the water for air. 




tadcpotes e w attached: to aleaf- 



Traae the life history of the frog. How long does it take for the frog to pass through 
this metamorphosis ? (Use the frog co.n:non to your locality to answer this question. ) 

Changes in the diet of the animal also occur ; the long, coiled 
intestine is transformed into a much shorter one. The animal. 



254 



HOW DO WE CLASSIFY ANIMALS? 



now insectivorous in its diet, becomes provided with tiny teeth and 
a mobile tongue, instead of the horny jaws used in scraping off 
algae. After the tail has been completely absorbed and the legs 
have become full grown, there is no further structural change, 

and the metamorphosis is 

complete. 

Practical Exercise 14. Make a 
series of diagrams to show changes 
in methods of breathing in the frog, 
from hatching to adult. 

Compare the metamorphosis of 
a frog with an insect. Can you 
find four stages in each : egg, larva, 
pupa, adult? 

Toad. One of the nearest 
relatives of the frog is the com- 
mon toad. Its ugly appear- 
ance has given it a bad name. 
Toads do not cause warts, and do much good in our gardens by 
eating harmful insects. Their eggs are laid in strings, and like those 
of the frog, are deposited in fresh- water ponds. As many as eleven 
thousand eggs have been laid by a single toad. The egg-laying 
season of the toad is later than that of the frog. Toad tadpoles 
differ from those of the frogs, by being darker in color, and 
having a more slender tail and a relatively larger body. 

Other amphibians. The tree frogs or tree toads are familiarly 
known to us in the early spring as the " peepers " of the swamps. 
They are among the earliest of the frogs to lay their eggs. During 




L. W. Brownell 
How does a toad differ from a frog? 




L. W. Brownell 



Why is the red salamander an amphibian? 



AMPHIBIA 



255 



adult life they spend most of their time on the trunks of trees. 
Another common amphibian is the newt, a salamander. This 
smooth-skinned, four-limbed animal, often incorrectly called a 
lizard, passes its larval lif e in the water, where it breathes by means 
of external gills. Later it loses its gills, becomes provided with 
lungs, and comes out on land, but after two years it goes back to 
the water again to lay its eggs. 

Some salamanders never have lungs, but breathe through the 
moist skin. Still other amphibians are the mud puppies, sirens 
or mud eels, and the axolotl. 

Practical Exercise 15. Name all the amphibians in your locality. Why is 
the frog an amphibian? What other animals outside the amphibians could 
you consider as amphibious animals ? 

Practical Exercise 16. Compare the life history of a toad with that of a 
frog. 

Amphibia. As the name indicates (amphi, both, and bios, life), 
members of this group live during their life history both in water 
and on land. In the earlier stages of their development they take 
oxygen into the blood by means of gills. When adult, however, 
they breathe by means of lungs. At all times, but especially 
during the winter, the skin serves as a breathing organ. The skin 
is soft and unprotected by bony plates or scales. The heart has 
three chambers : two auricles and one ventricle. Most amphib- 
ians undergo a metamorphosis, or change of form, the young 
being unlike the adults. About 1500 species are known. 



AMPHIBIA 



UrocCelct 



7 ^ 



A.T2LXr^X 





n^e^t 



Order 1. Urode'la. Amphibia having poorly developed appendages. Tail persistent 

through life. Examples : mud puppy, newt, salamander. 
Order 2. Anu'ra. Tail-less Amphibia, which undergo a marked metamorphosis, breathing by 

gills in larval state, by lungs in adult state. Examples : toad and frog. 



256 



HOW DO WE CLASSIFY ANIMALS? 



Self-Testing Exercise 

Frogs are adapted to their environment by having (1) 

feet and a thin skin filled with (2) (3) by means 

of which they (4) oxygen. The frog breathes air by means of 

(5). The short (6) leads into a bag-like (7) 

which in turn opens into a much-coiled small (8). The 

heart is (9) chambered (10) are laid in water and 

develop into (11) which breathe by (12). These 

are replaced by (13). The tadpole feeds on (14) 

(15), but the adult frog eats (16). A relative of the 

frog is the (17). It lays its eggs in (18) in the 

water while those of the frog are found in (19). Toads are of 

much (20) in gardens where they (21) (22) 

insects. Other examples of (23) are newts and salamanders. 



PROBLEM VII. WHAT ARE CHARACTERISTICS OF THE 
REPTILES? 

Turtles' adaptations for life. The turtles form a group, including 
both sea and land animals, the latter called tortoises. The body 

is short and broad, 
and is covered on 
the upper and lower 
sides by a bony 
framework of plates 
cemented to the true 
bone underneath. 
This shell is an adap- 
tation for protection. 
The long neck and 
powerful, horny jaws 
are factors in pro- 
curing food. Turtles 
have no teeth. Prey 
is seized and held 
by the jaws which 




Amer. Mus. of Natural Hist. 



How does the three-toed box turtle seem fitted to its 
environment ? 



LIZARDS 257 

I have sharp, chisel-like edges while the claws of the front legs are 
I used to tear the food. 

Turtles are very strong for their size. The stout legs carry 
I the animal slowly on land. In some water turtles the front limbs 
I are modified into flippers for swimming. The strong claws are 
I used for digging, especially at the egg-laying season, for some 
I turtles dig holes in sandy beaches in which the eggs are de- 
li posited. 

Turtles are mostly aquatic in habit. Among the exceptions 
I are the box tortoise and the giant tortoise of the Galapagos Islands. 
I Many of the salt-water turtles are of large size, the leatherback 
j| and the green turtle often weighing six hundred to seven hundred 
i! pounds each. 

Lizards. Lizards may be recognized b}^ their long body with 
I four legs of nearly equal size. The body is covered with scales. 
I The animal never lives in water, is active in habit, and does 
I not undergo a metamorphosis. Lizards are generally harmless 
I creatures, the poisonous Gila monster of New Mexico and Arizona 
being one exception. Lizards are of economic importance to man 
I) because they eat injurious insects. The iguana of Central America 
I and South America, growing to a length of three feet or more, has 
the distinction of being one of the few edible lizards. 







Wright Pierce 

The Gila monster is the only poisonous lizard in the United States. It is brilliantly colored in 
red and black. What may be the value of this coloring ? 



258 



HOW DO WE CLASSIFY ANIMALS? 



Snakes. Probably the most disliked and feared of all common 
animals are snakes. This feeling, however, is rarely deserved, 
for, on the whole, our common snakes are beneficial to man, 
for they live largely on injurious animals, such as rodents, insects, 
and slugs. 

Locomotion. Snakes are almost the only vertebrates without 
appendages. Although the limbs are absent, the pelvic and 
pectoral girdles are developed. The very long backbone is made 
up of a large number of vertebrae. As many as four hundred are 




Wright Pierce 

The rattlesnake is one of the few poisonous snakes. The snake is coiled, with 
rattlers buzzing, ready to strike. 



found in the boa constrictor. Ribs are attached to all the vertebrae 
in the region of the body cavity. They progress with a gliding 
motion caused by pulling and pushing the body along the ground, 
a leverage being obtained by means of the broad, flat scales, or 
scutes, on the under side of the body. 

Feeding habits. The mouth is a wide, slitlike opening extending 
nearly around the anterior end of the head, and is therefore capable 
of wide distention. A snake holds its prey by means of incurved 
teeth. In the poisonous snakes two of these teeth are hollow or 
grooved, and serve as a duct for the passage of poison. The 
poison glands are at the base of the curved fangs in the upper jaw. 



REPTILES 259 

The tongue, an organ of touch and taste, is very long and forked 
at the end. The food is swallowed whole, and pushed down by 
rhythmic contractions of the muscles surrounding the gullet. 
Snakes usually refuse other than living prey. 

Alligators and crocodiles. Crocodiles are mostly confined to 
Asia and Africa, while alligators are natives of North and South 
America. The chief structural difference between them is that 
the teeth in alligators are set in long sockets, while those of the 
crocodiles are not. Both of these lizardlike animals have broad, 
vertically flattened tails adapted to swimming. Their skins are 
very tough and are covered with bony scales. 




Amer. Mus. of Nat. Hist. 
Why is the alligator classified as a reptile ? 

Practical Exercise 17. Give a good definition of a reptile. What reptiles 
are common in your locality ? 

Practical Exercise 18. What is one character by which you can distinguish 
a reptile from an amphibian ? In what part of this country are reptiles most 
numerous ? Why ? 

Reptiles. These animals are characterized by having scales 
developed from the skin. In the turtle they have become bony 
and are connected with the internal skeleton. Reptiles always 
breathe by means of lungs, differing in this respect from the 
amphibians and fishes. They have the same temperature as their 
surroundings and usually hibernate as soon as winter comes. 
They show their relationship to birds by laying large eggs, 
incased in a leathery, limy shell. There are about 1500 known 
species. 



260 



HOW DO WE CLASSIFY ANIMALS? 



Cthelonioc 

turtle 



Lacertilicc 

1 X ^ ex ]p*ot^ 




Order 1. Chela' ' nia (turtles and tortoises). Flattened reptiles with body inclosed in bony 
case. No teeth or sternum (breastbone). Examples: snapping turtle, box tortoise. 

Order 2. Lacertil'ia (lizards). Body covered with scales, usually having two-paired ap- 
pendages. Examples : fence lizard, horned toad. 

Order 3. Ophid'ia (snakes). Body elongated, covered with scales. No limbs present. 
Examples : garter snake, rattlesnake. 

Order 4. Crocodil'ia. Fresh-water reptiles with elongated body and bony scales on skin. 
Two-paired limbs. Examples : alligator, crocodile. 

Self-Testing Exercise 

Reptiles are animals which have (1) or (2) plates 

developed from the (3). They always breathe by means of ! 

(4) (5), (6), (7), (8), 

and (9) are examples of reptiles. 



PROBLEM VIII. WHAT ARE THE CHARACTERISTICS OF 

BIRDS? 

Adaptations of birds. Birds are distinguished from all other 
animals by their covering of feathers and by the modification of 
the fore limb into a wing for flight. Hollow bones, feathers, and 
air sacs inside of the body cavity give buoyancy to the body and 
aid it in staying up in the air. The body is conically-shaped. 
The tail acts as a rudder. The bill is horny and adapted for 
securing food. The legs show variations for running, perching, 
scratching, or swimming. 

The wing is a modified arm, with the fingers very much reduced. 
To the posterior edge of the wing are fastened long quill feathers 
which overlap and make a broad, stiff surface for pressing against 
the air. The wing is jointed and moves in flight like a horizontal 
figure eight. Powerful breast muscles are attached to the wing 



ADAPTATIONS OF BIRDS 261 

bones and give great strength in movement. The rate of move- 
ment of the wing differs greatly in different birds. The wing of a 
bird is slightly concave on the lower surface when outstretched. 
Thus on the downward stroke of the wing more resistance is 
offered to the air. The soaring of birds is probably accomplished 
by very slight movements of the wings which result in making 
use of wind currents. 

The tail is sometimes used in balancing; its chief function, 
however, appears to be that of a rudder during flight. Most birds 
have under the skin of the tail a large oil gland, whence comes the 
supply of oil that is used in waterproofing the feathers when they 
preen themselves. 

■ Crown. 

-forehead 

.upper mandible 

neck— — „,._ J- ^J" ^1 

back— £ +******* -■■/' *~- lower mandible 

^ o./-' / H- throat 

rump. 

* ^ J>"'£^ibAr--/ —coverts 

tail coverts,^/- \ A^^^a^^x/ ^.^...........treast 

^yKfyJlL .- ahdamexi. 

l ^^0L - flanks 

^ ..toes 
hind toe. 

Find and list all the adaptations in this bird. Explain the value of each adaptation named. 




Thinly feathered and featherless areas can be found on the body 
of any bird, although these areas. are so well covered by the over- 
lapping feathers that no bare places are to be seen. There are 
i several kinds of feathers on the body of a bird. Soft down feathers 
| make a warm body covering ; larger feathers, known as contour 

H. BIO — 18 



262 



HOW DO WE CLASSIFY ANIMALS? 



feathers, give the rounded contour to the body. In the wings we 
find quill feathers ; these are adapted for service in flight by having 

long hollow shafts, 

the whole making a 

rttofri . light structure and 

^^ offering considerable 

resistance to the air. 
Feathers are devel- 
oped from the outer 
layer of the skin, and 
are formed in almost 
exactly the same 
manner as are the 
scales of a fish or a 
lizard. Feathers are 
shed or moulted one 
or more times dur- 
ing the year, and lost 
or broken feathers 
are replaced. Some 
birds moult twice a 
year, having differ- 
ent colored feathers 
in the summer and 
winter seasons. 
Many bones are hollow or have large spongy cavities. Some 
bones, notably the breastbone, are greatly developed in flying 
birds for the attachment of the muscles used in flight. 

The ankle of a bird is long and reptile-like and, like the foot, is 
covered with scales. The most extraordinary adaptations are 
found in the feet of various birds : some for perching, others for 
swimming, others for scratching, etc. By looking at the feet of a 
bird we are able to decide almost certainly its habitat, method of 
life, and perhaps its food. 

In the perching birds we find three toes in front and one behind, 
the hind toe playing an important part in clinging to the perch. 
The three toes in front curve around the perch^ often meeting the 




Wright Pierce 

Compare this bird with an airplane. In what ways are they 
similar, and in what ways different ? 



BIRDS 



263 



posterior toe, which is curved also. The tendons of the leg and 
foot are self-locking. In the flamingoes and other birds, which 
do not perch, balancing appears to be automatic, for these 
birds are able to maintain an upright position even when asleep. 
In swallows, rapid and untiring flyers, the feet are small. In 
the case of the parrots, where the foot is used for holding food, 
climbing, and clinging, we find the four-clawed toes arranged 
two in front and two behind. 

The form of the bill shows adaptation to a wonderful degree, 
varying greatly according to the habits of the bird. A duck has a 
flat bill for pushing through the mud and straining out the food ; 
a bird of prey has a curved or hooked beak for tearing ; the wood- 
pecker has a sharp, straight bill for piercing the bark of trees in 
search of the insect larvae underneath. Birds do not have teeth. 
The edge of the bill may 
appear to be toothed, as in 
some fish-eating birds ; how- 
ever, the projections are not 
true teeth. Frequently the 
tongue has sharp, toothlike 
edges which serve the same 
purpose as the curved teeth 
of the frog or snake. 

Respiration. The rate of 
respiration, of heartbeat, and 
the body temperature are all 
higher in the bird than in 
man. Man breathes sixteen 
or eighteen times a minute. 
Birds breathe from twenty to 
sixty times a minute. The 
lungs of birds are connected 
to large air sacs, found in the 
abdominal cavity of the body, 
which ,hold reserve air and 
help make the bird lighter. A bird may be compared to a high- 
pressure steam engine. In order to release the energy which it 







r""~ Wgk* 




hH 


It 


5 ; % 1 






■ ^ 



Wright Pierce 
What are the adaptations of the Golden eagle ? 



264 



HOW DO WE CLASSIFY ANIMALS? 



uses in flight, a large quantity of fuel which will oxidize quickly 
must be used. Birds are large eaters, and the digestive tract is 
fitted to digest the food quickly. As soon as the food is absorbed 
by the blood, it may be sent rapidly to the places where it is 
needed, by means of the strong four-chambered heart and large 
blood vessels. 

The high temperature of the bird is a direct result of this rapid 
oxidation; furthermore, the feathers and the oily skin form an 

insulation which 
does not readily 
permit the escape 
of heat. This in- 
sulating cover is 
of much use to the 
bird in its flights 
at high altitudes, 
where the temper- 
ature is often very 
low. 

The nervous 
system and the 
senses. The cen- 
tral nervous sys- 
tem of a bird is 
well developed. 
Attached to the 
fairly large brain 
is the spinal cord 
which extends the length of the body. From this cord nerves are 
given off. Sight is probably the best developed of the senses. 
The keen sight of a hawk is proverbial. Hearing is also well 
developed in most birds. The sense of smell does not appear to 
be well developed, and is especially deficient in seed-eating birds. 
Nesting habits. Among the most interesting of all instincts 
shown by birds are those of nest building. Birds incubate their 
eggs, that is, hatch them, by the heat of their bodies. Hence 
a nest is needed. The ostrich is an exception; it makes no 




Wright Pierce 

The sharp-edged, chisel-like bill of the woodpecker made these 
holes in the tree. Red-headed woodpeckers also have the un- 
usual habit of storing nuts of various kinds in the crevices and 
holes they make in the bark of certain trees. 









Wright Pierce 
What can you tell about the habits and characteristics of the birds which made these nests ? 

265 



266 



HOW DO WE CLASSIFY ANIMALS? 



nest, but lays its eggs on the ground. Birds immune from the 
attacks of enemies because of their isolation or their protective 
coloration (as the gulls and terns) build a rough nest among the 
rocks or on the beach. The eggs, especially those of the tern, are 
marked and colored so as to be almost indistinguishable from the 
rocks or sand on which they rest. Other birds have made their nest 
a place of refuge as well as a place to hatch the eggs. 

Care of the young. After the eggs have been hatched, the young 
birds in most cases are quite dependent upon the parents for 
food. Most young birds are prodigious eaters. As a result they 
grow very rapidly. It has been estimated that a young robin 
eats two or three times its own weight of food every day. In the 
case of the pigeons and some other birds, food is swallowed by 
the mother, partially digested in the crop, and then regurgitated 

into the mouths of 
the young nestlings. 
Relationship of 
birds and reptiles. 
The birds afford an 
interesting example 
of how the history 
of past ages of the 
earth has given a 
clue to the struc- 
tural relation which 
birds bear to other 
animals. Several 
years ago, two fossil 
skeletons were found 
in Europe of a bird- 
like creature which 
had not only wings 
and feathers, but 
also teeth and a lizardlike tail. From these fossil remains and 
certain structures (as scales) and habits (as the egg-laying habits), 
naturalists have concluded that birds and reptiles in distant 
times were closely related and that our existing birds probably 




Museum of Natural History 



The eggs of a dinosaur, a large land reptile which lived mil- 
lions of years ago. This nest of eighteen eggs was found in 
Mongolia. 



CLASSIFICATION OF BIRDS AND REPTILES 



267 



developed from a reptile-like ancestor many ages ago. The 
recently discovered eggs of the extinct dinosaurs are another link 
in the chain of relationship. 

Practical Exercise 19. Make a comprehensive definition of a bird. What 
evidences of relationship do you find between reptiles and birds? What 
particular adaptations would you expect to find in a bird of prey ? A swim- 
mer? A wader? 

Laboratory Exercise. Using the text as a guide, study a living 
bird to find: (1) adaptations for flight; (2) for food getting; (3) for 
protection. 

Ratitcte |CPasseres GaUteae TSaptores Cbaradnkfee 



Wdcrophires 

Svift,: 







climlSer^ parrots 





6acfpeckere cCove^ 



Order 1. Rati'tae. Running birds with no keeled breastbone. Examples : ostrich, casso- 
wary. 
Order 2. Pas'seres. Perching birds ; having three toes in front, one behind. Over one half 

of all species of birds are included in this order. Examples : a sparrow, thrush, swallow. 
Order 3. Galli'nae. Strong legs, feet adapted to scratching. Beak stout. Examples: 

jungle fowl, grouse, quail, domestic fowl. 
Order 4. Rapto'res. Birds of prey. Hooked beak. Strong claws. Examples : eagle, hawk, 

owl. 
Order 5. Limicolae. An order of the shore birds, wings long, thin, flat, and pointed. Legs 

usually very long. Bills are sometimes long. Examples : plover, snipe, sandpiper. 
Order 6. Longepennes. Drivers and swimmers. Legs short, toes webbed. Examples: 

gull, duck. 
Order 7. Colum'bae. Like Gallinae, but with weaker legs. Examples : dove, pigeon. 
Order 8. Pici. Woodpeckers. Two toes point forward, two backward, and adaptation 

for climbing. Long, strong bill. 
Order 9. Psittaci. Parrots. Hooked beak and fleshy tongue. 
Order 10. Coccyges. Birds, with powerful beaks, using their feet as a means of progression. 

Examples : kingfisher, toucan, and cuckoo. 
Order 11. Macrochires. Birds having long, pointed wings, without scales on metatarsus. 

Examples : swift, humming bird, and goatsucker. 

Self-Testing Exercise 

Birds are characterized by having an (1) covering of 

(2) ; (3) ; (4) modified for (5) in 



268 



HOW DO WE CLASSIFY ANIMALS? 



(6) ; (7) bones ; (8) on the legs (which show 

their (9) to the reptiles) ; (10) but no true 

(11) ; (12) temperature ; a (13). They lay 

(14) covered with a (15) (16). The 

(17) in leg and bill show clearly what kind of (18) 

the bird leads and the (19) of (20) it uses. 



PROBLEM IX. 



WHAT ARE THE CHARACTERISTICS OF 
MAMMALS? 



Practical Exercise 20. Make brief descriptions in your workbook of two 
mammals such as a cat and a horse. How do they differ? How are they 
similar ? 

Mammals. Mammals are characterized by being warm blooded, 
by having a four-chambered heart, a diaphragm, and well-developed 
lungs. The most characteristic features, however, are that they 

have a hairy cover- 
ing at some period 
of their existence 
and bring forth their 
young alive. The 
young are nourished 
on milk secreted by 
glands known as the 
mammary glands ; 
hence the term 
"mammals." Mam- 
mals are considered 
the highest of verte- 
brate animals, not 
only because of their complicated structure, but because of 
their mental development. 

Individual project. Visit a museum and study the skeletons and 
mounted bodies of a seal and of a whale. Why do we consider these 
animals mammals rather than fishes or amphibians? 

Carnivores. Carnivorous mammals are to a large extent flesh 
eaters. In a wild state they hunt their prey, which is caught and 
torn with the aid of well-developed claws and long, sharp canine 
teeth. 




U. S. Bureau of Biological Survey 
What kind of food does the black bear eat ? 



MAMMALS 



269 




All flesh-eating 
mammals are wan- 
dering hunters ; 
many, as the bear 
and lion, have 
homes or dens to 
which they retreat . 
Some, as bears and 
raccoons, live part 
of the time upon 
berries and fruit. 

Rodents. Mam- 
mals known as 
rodents have the 
teeth so modified 
that on both up- 
per and lower jaws 
two prominent 
teeth, incisors, are 
used for gnawing. 
These teeth keep 
their chisel-like 
edges because the back part of the teeth is softer and wears 
away more rapidly than the front part. The canine or dog teeth 
are lacking. We are all familiar with the destructive gnawing 
qualities of one of the commonest of all rodents, the rat. 

Ungulates: hoofed mammals. This group includes most of 
the domesticated animals, as the horse, cow, sheep, and pig. 
Many of these animals came under the subjugating influence of 
man and now they form an important part of the world's wealth. 

The order of ungulates is a very large one. It is characterized 
by the fact that the nails have grown down and become thickened 
as hoofs. In some cases only two (the third and fourth) toes are 
largely developed. Such animals have a cleft hoof, as the ox, 
deer, sheep, and pigs. They are the even-toed ungulates. The 
deer family contains the largest number of species and individuals 
among our native forms, and in fact the world over. Among them 







1 W 


mmi ' '"^ 


F^**!x. 











of Biological Survey 



The beaver is a rodent. 
How does he differ from 
other mammals ? What 
kinds of food does he eat? 



U. S. Bureau of Biological Survey 



270 



HOW DO WE CLASSIFY ANIMALS? 



are the common Virginia deer of the Eastern states, and the 
moose and antelope. The bison, or buffalo, is closely related 
to the deer. Formerly bisons existed in enormous numbers on 
our Western plains. They are now almost extinct. 

Primates. Man is placed in the highest order of mammals, the 
primates, because he walks upright and the fore appendages 
(arm) are each provided with hands for grasping. Nails instead 
of claws are present. The primates have the same characteristics 
as other mammals, but may be said to be superior to them in 
having a more highly developed brain and nervous system. 

Practical Exercise 21. Name a common example of each order of mammals 
found in your locality. What are the chief characteristics of the carnivora? 




CetcxCea 




Cfeiroptera 

Ccti^mvorar 



Sirema 



5?octentia_/ \_ 



T <C£> UJ 

Insectivom 




XCndLclcita 




*■ - C_ 



Order 1. Edentata. Toothless or with very simple teeth. Examples: anteater, sloth, 

armadillo. 
Order 2. Cetacea. Adapted to marine life. Examples: whale, porpoise. 
Order 3. Sirenia. Fishlike in form; pectoral limbs paddle-like. Examples: manatee, 

dugong. 
Order 4. Rodentia. Incisor teeth chisel-shaped, usually two above and two below. Ex- 
amples : beaver, rat, porcupine, rabbit, squirrel. 
Order 5. Ungulata. Hoofs ; teeth adapted for grinding. Examples : (a) odd-toed : horse, 

rhinoceros, tapir ; (6) even-toed : ox, pig, sheep, deer. 
Order 6. Insectivora. Small, insect-eating, furry or spiny covered; long snout. Example: 

mole. 
Order 7. Carnivora. Long canine teeth, sharp and long claws. Examples: dog, cat, lion, 

bear, seal, and sea lion. 
Order 8. Chiroptera. Fore limbs adapted to flight, teeth pointed. Example: bat. 
Order 9. Primates. Erect or nearly so, fore appendage provided with hand having nails. 

Examples : monkey, ape. Anatomically, man is placed with this group of mammals. 



STORY TOLD BY FOSSILS 



271 



The rodents? The ungulates? Which group is most useful in your locality? 
Most harmful? Which members should be destroyed? Protected? 



Self-Testing Exercise 

Mammals are characterized by having (1) blood, 

(2) heart, (3), and a muscular wall just below these organs 

called a (4). Mammals have (5) on the body and 

(6) their young. The important orders are the (7) 

or gnawers, the (8) or hoofed animals, the (9), 

with sharp teeth, and the (10), which includes man. 



PROBLEM X. WHAT STORY IS TOLD BY THE FOSSILS? 

We have learned that animals may be arranged in groups, 
beginning with very simple one-celled forms and culminating with 
man himself. These groups are believed by some scientists to rep- 
resent, in a way, different stages in the evolution or development of 
life on the earth. 

We know that in the millions of years that life has existed on 
the earth that there have been many changes. According to present- 
day evidences, living things at first were very simple in structure, 
but as time went on more and more complex types appeared. 

Many of you have probably had the interesting experience of 
finding in rocks, not far from the shore, shells or other evidences 
of life. Sometimes these were simply 
casts in rock which once held the 
remains of animals and plants. In- 
frequently, we find actual preserved 
specimens, as insects in amber. All 
these things are called fossils. If we 
study the geology of the rocks id 
which fossils are found, we learn that 
these rocks were once laid down under 
water in layers, and that the animal 
or plant remains were caught there, 

^ & > The Archaeopteryx is the earliest 

then COVered Up, and preserved. We known bird. According to fossil skele- 

i n i xi ±_ j i i j i tons » it was the size of a crow and had 

also find that the rocks nearer the teeth. 




272 



HOW DO WE CLASSIFY ANIMALS? 



surface contain remains of living things that inhabited the earth in 
fairly recent time, while those deeper in the earth contain fossils 
of animals and plants that are unlike any that are now living, 
and are, therefore, thought to have lived millions of years ago. 
In this way scientists have learned that the earliest forms of life 
upon the earth were very simple, and that gradually more and 
more complex forms appeared, as the rocks formed latest in 
time show the most highly developed forms of plant and animal 
life. 

Some evidences of ancient forms of life. From a study of 
fossils from various rock formations all over the world the following 
very interesting facts have been discovered : that the oldest rocks 

contain very simple 
plants and animals, al- 
most all marine ; that 
there came a period in 
which many kinds of 
invertebrates lived, at 
this time land plants 
appeared ; then came 
the age of fishes, many 
of which were great 
armored beasts, long 
since gone. Still later 
we have an age of am- 
phibians. During this 
last period great forests 
flourished from which 
our anthracite coal beds 
were formed. Then 
came a time when mon- 
strous reptiles roamed 
over the earth, some 
of them 60 to 70 feet 
in length. Later these 
great animals, dinosaurs, vanished and huge batlike animals and 
birds appeared. During this time the beginnings of our modern 




Alma Chesnut — Amer. Nature Ass' 



Unearthing the bones of huge animals which at one 
time lived in Wyoming. These bones are relics of a 
mighty race that perished in forgotten ages. 



GEOLOGIC HISTORY OF THE HORSE 



273 



mammalian life came into existence. All of these changes have 
taken tens, or more likely hundreds of millions of years, as we can tell 
from the thickness of the rock deposits in which the fossils are found. 




Amer. Mus. of Nat. Hist. 
This giant dinosaur, over sixty feet long, lived in Wyoming millions of years ago. 

Other evidences of organic evolution. Evidences of changes 
in form through past ages have been found in the study of the 
elephants, which have changed from a trunkless and relatively 
small animal to the huge elephant of today. The great saber- 
toothed tiger, which once roamed the fields of California, has 
given way to the modern type. 

In certain of the higher animals we find traces of organs that 
are no longer used, although they may have been of value to 
the animals in the past. The appendix in man is small and use- 
less, but in some animals, it is large and performs an important 
digestive function. The muscles of the ears of human beings are 
useless, but in lower animals they are of great value in aiding the 
hearing. 

Geologic history of the horse. That developmental changes 
have taken place in certain types of animals is shown by a study 
of a series of fossil horse skeletons, which have been reconstructed 
so that we can pretty certainly tell what ancient horses look like. 

The fossils of leg bones show that, ages ago, the remote ancestors 
of the horse were probably small animals the size of a domestic 
cat, with five-toed feet. The earliest horse we have knowledge 



274 



HOW DO WE CLASSIFY ANIMALS? 



of had four toes on the fore and three toes on the hind feet. Thou- 
sands of years later there existed a larger horse, the size of a sheep, 

with three toes on each foot. Through 
a series of changes there was eventually 
produced our present horse, an animal 
with legs adapted for rapid locomotion, 
with feet particularly fitted for life in 
open fields, and with teeth which serve 
well to seize and grind herbage. 

Practical Exercise 22. From outside sources 
construct a diagram to show the different geologic 
ages in this country. In what kind of rocks 
would you look for fossils? Visit a museum 
and describe some evidences of development seen 
therein. What examples of change have you 
seen in the world today ? List them. 



Self-Testing Exercise 

The (1) forms of (2) 

on the earth are believed to have been 
very (3), while those that devel- 
oped (4) are more (5). 

(6) or remains of animals and 

plants (7) in (8) tell us the 

story of (9) of life on the earth. 

Once, ages ago, there existed (10) 

horses having (11) toes on the fore 

feet. Later, as life on the earth changed, 
there was a gradual development in these | 

(12) so that today we have horses 

with (13) toe, and longer legs fitted 

for more (14) locomotion. 




Tfesobippccs 

Cohippus Protorohxppus 

Redrawn from Photo ofAmer. 
Mus. of Nat. Hist. 

In what ways has the horse 
changed through the ages ? 



PROBLEM XI. WHAT IS MAN'S PLACE IN NATURE? 

There is no doubt that man is young compared to some animals, 
but he is vastly older than was once believed. Very good evi- 
dences in the form of skulls found in the caves of France and the 
gravel pits of England show that man has lived on the earth tens of 



; 



WHAT IS MAN'S PLACE IN NATURE? 



275 



thousands, probably hundreds of thousands of years, 500,000 to 
1,000,000 years being the latest estimate. 

Parts of skeletons found in Java and Europe show a type of 
man much lower than any savage living today. Arrowheads, of 
a kind older than any made within the memory of man, have 
been found among the bones of extinct bisons under the soil of 
our Western plains. Races of men must have once existed there 
who have now vanished. 

Evidences in the forms of fossil bones and parts of skulls show 
also that man has been changing during these many centuries. 
His arms used to be longer, his frame more massive, his jaw and 
face more ape-like. This does not mean that man has ascended 
from an ape ; it simply shows a gradual development or evolution 
through many thousands of years from some stock which gave 
rise to the apes and to man separately. Just as we now have been 
able artificially to improve plants and animals through scientific 
breeding, so Mother Nature has, by a hit-and-miss method, im- 
proved the breed of man on the earth. How these changes have 
been brought about is only conjecture, but we do know that there 
are great differences between the men on the earth today and those 




Amer. Mus. of Nat. Hist. 

From fossils that have been discovered in many parts of the world, Dr. J. H. McGregor has given 
us his idea of the probable appearance of prehistoric man in different stages of development. 

of yesterday. But there are also as great structural differences 
between the Bushmen of Africa and the white men of England or 



276 HOW DO WE CLASSIFY ANIMALS? 

America as there are between those same Bushmen and some of 
the early races of man. Undoubtedly there once lived upon the 
earth races of men who were much lower in their mental organi- 
zation than are the present inhabitants. If we follow the early 
history of man upon the earth, we find that at first he must have 
been little better than one of the higher vertebrates. He was a 
nomad, wandering from place to place, living upon whatever ani- 
mals he could kill with his hands and whatever edible plants he 
found. Gradually, he learned to use weapons to kill his prey, 
first using rough stone implements for this purpose. As man be- 
came more civilized, implements of bronze and of iron were used. 
About this time the subjugation and domestication of animals 
began to take place. Man then began to cultivate the fields, 
and to have a fixed place of abode other than a cave. The be- 
ginnings of civilization were long ago, but even today the world 
is not entirely civilized. 

Demonstration. The skeleton of man compared with other mam- 
mals. Use skeletons of a fish, frog, bird, dog or cat, and man. If 
this material is not available in school, visit a museum. Observe the 
kinds and places of the different bones in body of each skeleton. In 
what ways do the various skeletons agree ? How do they differ ? 

Why is man a mammal ? Although we know that man is sepa- 
rated by a gap from all other animals by the power of speech, we 
must ask where we are to place him structurally. If we attempt 
to classify man, we see at once he must be grouped with the 
vertebrate animals because of his possession of a vertebral column. 
Evidently, too, he is a mammal, because the young are nourished 
by milk secreted by the mother and because his body has at least 
a partial covering of hair. Among the different orders of mammals 
man most closely resembles anatomically the primates to which 
the monkeys and apes belong. 

If we compare several skeletons of different mammals, we 
find certain definite likenesses in body plan. In the first place, 
all vertebrates have the same general parts of the skeleton : the 
skull, vertebral column, the front and rear appendages, and the 
bony girdles, pectoral (shoulder) and pelvic (hip), which connect 
the appendages with the main or axial skeleton. Then, too, they 



TESTS 277 

all have the same general plan of digestion system, the same kinds 
of circulatory, respiratory, and excreting systems, although here 
more variations are evident among the fishes, amphibians, and 
mammals. Even the nervous system, which seemingly ought to 
show very great changes in structure, is not as different as one 
might expect. Moreover, if you compare the skeleton of an ape 
with that of man, you notice some striking likenesses which set 
their two skeletons off from those of the other vertebrates. Both 
show a more or less upright posture ; they both have well-marked 
fingers and toes ; the general shape of the head is similar, the 
pectoral and pelvic girdles are markedly alike, and a detailed 
study would show many other similarities. If we follow the same 
principles for the study of relationships here as we have in other 
animals, we are forced to the conclusion of a close structural re- 
lationship between the apes and man. 

Self-Testing Exercise 

Man is a (1) because he has a backbone. Man is a 

(2) because he has hair, and the (3) are nourished 

by (4) secreted by the (5) (6). He is a 

(7) and must be placed anatomically with the (8). 

This does not mean he is (9) from the (10), for 

man has existed in a (11) state for (12), perhaps 

(13) of thousands of years. 

Review Summary 

Test your knowledge of the unit by: (1) rechecking the survey questions; 
(2) performing all the assigned exercises ; (3) checking with the teacher your 
answers on the various tests and trying again the ones you missed; and, 
finally, (4) making an outline and filling it in as fully as possible for your note- 
book. 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write the numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue state- 
' ments. Your grade = number of right answers X 2. 

I. Classification of living things is based: (1) upon likeness and 

' differences in structure; (2) upon relationships shown by analogies 

I in use uf parts ; (3) upon relationships shown by homologies in struc- 

i ture ; (4) upon the place where they live ; (5) on the way in which 

they grow. 

H. BIO — 19 



278 HOW DO WE CLASSIFY ANIMALS? 

II. The protozoans (6) always have cilia; (7) are single-celled 
animals; (8) never live in the water; (9) reproduce by dividing; 
(10) reproduce by budding. 

III. The coelenterates (11) live in the ocean; (12) have baglike 
bodies with a mouth at one end; (13) are usually fixed and do not 
move from place to place ; (14) may show an alternation of generations ; 
(15) include corals, sea anemones, and hydra. 

IV. The arthropods (16) have no definite number of legs; (17) al- 
ways have a limy shell; (18) have an exoskeleton; (19) have jointed 
legs and jointed body; (20) have compound eyes. 

V. Mollusks (21) are soft-bodied animals; (22) always have a 
shell ; (23) usually have a shell ; (24) live only on land ; (25) include 
snails, oysters, clams, and squids. 

VI. Fishes (26) are the only animals that live in the water; 
(27) have their limbs modified into fins; (28) breathe by taking 
oxygen out of water by means of gills ; (29) use the ear as a balancing 
organ ; (30) lay many eggs which are fertilized outside the body. 

VII. Amphibians (31) include turtles, snakes, and tortoises; 
(32) always have moist skin with no scales in it ; (33) often undergo 
a metamorphosis, part of the life being in the water and part on land ; 
(34) always have both lungs and gills at the same time in their life 
history ; (35) include the toads, frogs, and salamanders. 

VIII. Reptiles (36) have no teeth; (37) are never poisonous; 
(38) always have scales on the skin; (39) always breathe by lungs; 
(40) show their relationship to birds by laying eggs with shells. 

IX. Birds (41) show, by scales on their legs, relationship to reptiles ; 
(42) have modified arms or forelegs which are used in flying ; (43) al- 
ways build a nest in which are laid many eggs ; (44) have a four- 
chambered heart ; (45) have a skeleton composed of light and hollow 
bones, with large breastbone to which wing muscles are attached. 

X. Mammals (46) are at the top of the evolutionary scale ; (47) have 
a four-chambered heart, a more or less heavy covering of hair, and 
suckle their young ; (48) always stand erect ; (49) are found as the 
most recent fossils ; (50) include man. 

Achievement Test 
1. What is the name of at least one animal from each of the phyla 
of the invertebrates and the vertebrates ? 



TESTS 



279 



2. What are the differences between spiders and insects? 

3. Where would you look for hydra, crayfish, clams, and toads? 

4. How can you distinguish between an amphibian and a reptile ? 

5. What is the life history of a frog common in your locality? 

6. Where and what fossils may be found in your locality? 



Practical Problems 

1. Make a collection of all invertebrates that you can find in your 
community. Classify them and arrange them in evolutionary order. 

2. Fill out the following table. 



Structures 


Fish 


Amphibian 


Reptile 


Bird 


Mammal 


Organs of 
digestion 












Protective 
structures 












Locomotion 












Organs of 
breathing 












Organs of 
excretion 












Parts of nervous 
system 










1 


Sense organs 













Useful Reference Books 



Allen, Birds and Their Attributes. (Marshal Jones Co. 1925.) 
Ditmars, Reptile Book. (Doubleday, Doran & Co.) 
Dickerson, Frog Book. (Doubleday, Doran & Co.) 
Hornaday, American Natural History. (Charles Scribner's Sons.) 
Jordan and Evermann, American Food and Game Fishes. (Double- 
day, Doran & Co. 1923.) 
Lucas, Animals of the Past. (Amer. Mus. of Nat. Hist., N. Y. 1922.) 
Osborn, Men of the Old Stone Age. (Charles Scribner's Sons. 1919.) 
Palmer, Field Book of Nature Study. (Comstock Publishing Co. 1927.) 
Plunkett, Outlines of Modern Biology. (Henry Holt & Co. 1930.) 
Reed, Bird Guide. (Doubleday, Doran & Co, 1925.) 




SURVEY QUESTIONS 

Do you know how plants are helpful or harmful to one another ? What 
is a balanced aquarium? What is an oxygen cycle? A carbon cycle? 
What do you understand by symbiosis? What are parasites? What 
factors caused the type of vegetation shown in this desert in Arizona ? 



Photo by Frank M. Wheat 



UNIT IX 



WHAT EFFECTS HAVE THE SURROUNDINGS ON THE 
LIVES OF PLANTS AND ANIMALS? 

Preview. If bees, in their search for nectar, visited the flowers 
of an apple tree, they would make possible the development of 
apples on this tree. This development might be hindered by 
other insects which prey upon ripening fruit, in which case man 
may step in, and with a poisonous spray kill the insects and thus 
save the fruit. 

But how did the bees benefit by this visit? They obtained 
nectar to make into honey, and pollen to make into bee bread 
for feeding the young. These will in turn replenish the hive the 

280 



i 



PREVIEW 281 

following year with more workers, that will make money for 
man, unless some prowling animal robber gets it first. Charles 
Darwin saw this interrelationship of plant and animal as a chain 
of happenings when he pointed out that the size of the clover 
crop in England depended upon the number of cats in a given 
region. His friend Huxley immediately went him one better and 
said the clover crop depended upon the number of old maids. 
When asked to explain, he gave the following chain of events. 
Old maids keep cats, cats prey upon mice, mice eat bumblebees 
and also provide them with places to build their nests, bumble- 
bees pollinate clover, and on this pollination depends the size of 
the next year's crop. A perfectly logical chain of events ! 

This unit will explain to us some of these interrelationships 
between plants and animals and may also show us how man some- 
times interrupts or displaces a link in the chain of interrelation- 
ships, which results in changing completely the fauna x or flora 2 of 
a region. The best example of this perhaps is the case of the man 
in Australia who wanted a bit of watercress to remind him of the 
old days in bonny England. Today, the rivers of Australia are 
choked with this same cress, which, having no enemies and finding 
conditions favorable, has literally overrun the brooks and rivers. 

We cannot fail to see that some animals and plants are fitted to 
live under conditions totally unsuitable for others. A fish could 
not live under the same conditions as a lizard, nor would we expect 
to find seaweeds growing in desert places where cactuses are 
found. Such things are quite evident, and if we travel in this 
vast country of ours we shall also find that plants and animals 
live in more or less different communities, and that there are dif- 
ferent climatic zones, in which, because of common needs, certain 
types of animal or plant life are always found. Such zones can 
be seen particularly well on a mountainside. Any one who has 
climbed the Katahdin mountain in Maine, or Mt. Washington in 
New Hampshire, or any 10,000-foot peak of the Rockies or Sierra 
Nevada, has had the experience of working his way through forests 
out into an area of stunted trees and finally out on the bare rocks 

1 Fauna (f 6'na) : the animals of a given region. 

2 Flora (flo'rd) : the native plants of a given region. 



282 LIVES OF PLANTS AND ANIMALS 

above the timber line. We might think that these different regions 
(life zones) were due entirely to temperature. On the mountain- 
side this is largely true, but we find that all the factors we have 
already discussed are at work determining the places where living 
things shall be found. The amount of water present in the soil, 
the kinds of soils there, the ranges in the temperature, the wind, 
and many other factors play their parts. One big problem in the 
geographical distribution of organisms is to find, first, adaptations 
of organisms for life in various localities, and then the place 
where a certain kind of living thing has made its start in an area, 
and finally how life spreads from this area to other areas. 

On the whole, nature establishes a balance in life and there 
is give and take between all living things. That part of biology 
which deals with the relationships of organisms to each other and 
to their environments is called ecology. 

PROBLEM I. WHAT GENERAL BIOLOGICAL RELATIONS 
EXIST BETWEEN PLANTS AND ANIMALS? 

Each place where plants and animals are found living togethei 
supports a characteristic community of plants and animals. This 
living together seems to be determined largely by the conditions 
of the environment in which they are placed. Groups living 
together in a pond or slow-flowing stream will be quite different 
from groups living in a rapid mountain stream or in the ocean. The 
communities of animals and plants living in dry or desert localities 
would differ to a still greater extent from any of those first men- 
tioned. Only certain animals and plants will five and flourish in an 
indoor aquarium, but in all such groups the animals and plants 
living together have certain fundamental relationships to each other 
and to their surroundings. 

Study of a balanced aquarium. Perhaps the best way for us 
to understand this relation between plants and animals is to 
study an aquarium in which plants and animals five and in 
which a balance has been established between the plant fife on 
one side and animal life on the other. Here we see many evidences 
of the relationship between the environment and the living things 
in the water. The plants are buoyed up by the water, they do not 



A BALANCED AQUARIUM 



283 




have strong stems, and the leaves are usually divided and present 
little resistance to the water. The roots are small and are not of 
much use as an anchor. The fish are obviously adapted for life 
in the water, as we have already seen. Even the snails have 
adaptations for their life in the water. 

We have learned that green plants, in favorable conditions of 
sunlight, heat, moisture, and with a supply of raw food materials, 
give off oxygen as a by-product while manufacturing food in their 
green cells. We know 
the necessary raw ma- 
terials for carbohydrate 
manufacture are carbon 
dioxide and water, while 
nitrogenous material is 
necessary for the making 
of proteins within the 
plant. In previous ex- 
periments we have 
proved that carbon di- 
oxide is given off by 
living things when oxida- 
tion occurs in the body. The crawling snails and the swimming 
fish give off carbon dioxide which is dissolved in the water ; the 
plants themselves, at all times, oxidize food within their bodies, 
and so must pass off some carbon dioxide. The green plants in 
the daytime use up the carbon dioxide obtained from the various 
sources and, with the water which they take in, manufacture 
carbohydrates. While this process is going on, oxygen is given off 
to the water of the aquarium, and is used by the animals there. 

The plants are continually growing, but the snails and fish 
eat parts of the plants. Thus the plant life gives food to the 
animals within the aquarium. The animals give off certain 
nitrogenous wastes. These materials, with other nitrogenous 
matter from dead animals and parts of the plants, form part of 
the raw material used for protein manufacture in the plant. This 
nitrogenous matter is prepared for use by several different kinds 
of bacteria which break down the dead bodies and change the 



Why will it not be necessary to change the water in this 
aquarium ? 



284 



LIVES OF PLANTS AND ANIMALS 



material into soluble nitrates which can be absorbed by the plants. 
The green plants manufacture food, the animals eat the plants 
and give off carbon dioxide and nitrogenous waste, from which the 
plants in turn make more food and living matter. The plants 
give oxygen to the animals, and the animals give carbon dioxide 
to the plants. Thus a balance exists between the plants and 
animals in the aquarium. 

Practical Exercise 1. Make a debit and credit balance sheet illustrating the 
relations existing in a balanced aquarium. 

What would be the condition of the balance sheet if the aquarium were 
put in a dark room? If several extra snails and fish were introduced? 

Relations between green plants and animals. What goes on 
in the aquarium is an example of the relation existing between all 
green plants and animals. Everywhere in the world green plants 
are making food which becomes, sooner or later, the food of 
animals. Man does not feed to a great extent upon leaves, but 
he eats many roots, stems, fruits, and seeds. When he does not 
feed directly upon plants, he eats the flesh of plant -eating animals, 
which in turn feed directly upon plants. And so it is the world 
over ; the plants are the food makers and supply the animals. 



carbon dioxide 

(CO*) 



Ca ^ ya< f dde Cco^ 



*<***(**>) 



ammonia 



PLANTS 

with chlorophyll 

"build "food, which 

contains stored. 

energy obtained 

•fr-om the, 

STCCT2 



energy from the sun 



simple salts 

/ N 




•^ixte-T*' 



ammonia 

^CNHi> 



energy released 



Plants and animals on the earth show the same relation to each other as do the plants and 
animals in a balanced aquarium. Can you explain, with the aid of the diagram, why this is true ? 



This is well seen in the distribution of grazing animals in relation i 
to forage crops. Green plants also give to the atmosphere every 
day a very considerable amount of ox} r gen, which the animals use. 



CARBON AND OXYGEN CYCLES 285 

Self-Testing Exercise 

(1) and (2) live together in communities. Such a 

place is called a (3). A balanced aquarium shows the 

(4) between animals and plants, the former give (5) 

(6), and (7) wastes to the plants which in turn 

(8) organic food which the (9) (10). 

This illustrates the give and take between plants and animals in the 
(11). 

PROBLEM II. WHAT DO WE MEAN BY THE NITROGEN, 
OXYGEN, AND CARBON CYCLES IN NATURE? 

Nitrogen cycle. The animals supply much of the carbon dioxide 
that the plant uses in carbohydrate making. They supply some of 
the nitrogenous matter used by the plants, another part being 
given the plants from the dead bodies of other plants, and still 
another part being prepared from the nitrogen of the air through 
the agency of bacteria which live upon the roots of certain plants. 
These bacteria are the only organisms that can take nitrogen from 
the air. Thus, in spite of all the nitrogen in the atmosphere, 
plants and animals are limited in the amount available. Eaten 
in protein food by an animal, nitrogen may be given off as nitroge- 
nous waste, get into the soil, and be taken up by a plant through 
the roots. Eventually the nitrogen forms part of the food supply 
in the body of the plant, and then may become part of its living 
matter. When the plant dies, the nitrogen is returned to the soil. 
Thus the usable nitrogen is kept in circulation. 1 

Practical Exercise 2. Illustrate what is meant by the nitrogen cycle with 
reference to your own environment. 

Make a diagram to show the way the nitrogen cycle works out in life on 
the earth. 

Carbon and oxygen cycles. There are also two other cycles 
in nature that are easily seen. Oxygen dissolved in the water is 
taken up by the fish in the aquarium, and is released in the form of 
an oxide of carbon or carbon dioxide. In this form it is taken 

*A small amount of nitrogen gas is returned to the atmosphere by the action of 
the decomposing bacteria on the ammonia compounds in the soil. (See figure of 
nitrogen cycle.) 



286 LIVES OF PLANTS AND ANIMALS 




Cerrboix 



How does the diagram of an amoeba, or head of a fish, or a cross section through the 

by green plants in the aquarium and during the starch-making 
process in the sunlight it is released as a by-product in the form 
of pure oxygen gas. It is now in the water ready for the fish to 
use again. This same process is repeated on a large scale wherever 
we find green plants, sunlight, and animals. 

The carbon cycle can also easily be shown. The fish in the 
aquarium eats some of the green plant, thus getting carbohydrate 
food which contains the element, carbon. As they swim about 
releasing energy they oxidize the carbohydrate food in their 
bodies and thus liberate the carbon in the form of carbon dioxide. 
This gas is used by the green plant in the sunlight to build carbo- 
hydrates and the cycle is completed again. Of course, the aqua- 
rium shows what goes on in a larger way in the world of living things. 

Practical Exercise 3. After carefully studying the text make a diagram in 
the form of a circle to illustrate the way the carbon cycle exists in nature. Use 
arrows. Make a second diagram to show the oxygen cycle in nature. 

Self -Test Exercise 

The (1) available for plant and animals is (2) over 

and over again by plants by making (3) (4). Cer- 
tain (5) break down substances containing (6) and 

put it into the (7) as (S) organic material. Then 

green plants take it up and (9) it into (10) food 

and (11) matter. There are (12) and (13) 

cycles in nature. Oxygen is given off by (14) plants, is used 

by (15). and breathed out as an (16) of carbon. 

Carbon is given off into the atmosphere by animals as (17) 

(18) and is used by (19) plants to manufacture 

(20). In such form it is (21) by animals and after 



SYMBIOSIS 



287 




en 



body of an insect, with the lower epidermis of a leaf show that living things breathe? 

being (22) in the body is passed into the air again as 

(23) (24), thus completing the cycle. 



i PROBLEM III. WHAT IS SYMBIOSIS AND HOW DOES IT DIFFER 
FROM PARASITISM? 

Symbiosis. Plants and animals are seen in a general way to 
i be of mutual advantage to each other. Some plants, called 
i lichens, show this mutual partnership in the following interesting 
way. A lichen is composed of two kinds of plants, one of which 
at least may live alone, but the two plants have formed a partner- 
j ship for life, and have divided the duties of such life between them. 
In most lichens the alga, a green plant, forms starch and nourishes 
the fungus. The fungus, in turn, produces spores, by means of 
I which new lichens are started in life ; moreover, the alga is 
> usually protected by the fungus, which is stronger in structure 
\ than the green part of the combination. This process of living 
together for mutual advantage is called symbiosis (sim-bi-o'sis). 
Some animals also combine with plants ; for example, the hydra 
I with certain of the one-celled algae. 
Animals also frequently live in 
i this relation to each other, the 
tiny protozoans living in the diges- 
tive tracts of the termites or white 
ants. These little animals act as 
digestive cells for the termites, 
making it possible for them to 
digest the wood fibers on which they live. In return these proto- 
zoans are protected by their hosts. A somewhat similar situa- 




Algae and fungi in a lichen, 
relationship. 



fungus 

Explain this 



288 



LIVES OF PLANTS AND ANIMALS 



■PSs 








•If - 


***£ ,.:**:.>. ^*i 



Lichen on a rock. 



i. >F. Brownell 

How do lichens differ from other 
plants ? 



tion prevails in our own 
large intestine, where 
certain types of useful 
bacteria live. They help 
keep down the putrefy- 
ing bacteria while receiv- 
ing a home and food in 
return. Other examples 
are the bacteria which 
live symbiotically in the 
roots of certain plants; 
and the sea anemones 
which are carried around 
on the backs of some 
hermit crabs to places 
where food is plentiful, and they aid the crab in protecting it from 
its enemies. In a general way the food relations between green 
plants and animals may be said to show a symbiotic relationship, 

because the plants 
could not make food 
without the wastes 
from the animals, 
and the animals 
could not exist with- 
out foods made by 
green plants. 

Parasitism. Not 
all life is give and 
take. Some plants 
and animals live at 
the expense of others, 
giving nothing and 
taking all. Such 
plants and animals 
'right pierce are known as para- 

Mistletoe on the branches of a sycamore tree. Notice that sites. Examples are 
the branches to the left bear no leaves. They have been . 

killed by the parasite. seen in the dodder 




MAN AND THE BALANCE OF LIFE 289 

and mistletoe among plants, and many insects and worms, among 
animals. In every case, the parasite lives on another plant or 
animal known as its host. In some cases, the host is a temporary 
one, and in others, it is a permanent one, the parasite remaining 
with it until death. Many plant and animal diseases are caused by 
parasites, and man has come into the picture to such an extent that 
he is now engaged in wiping parasitic disease off the face of the 
earth. 

Practical Exercise 4. Give as many examples of symbiosis as you can, using 
references and museum material. Explain how symbiosis in a large sense 
exists in the world about you. 

Self-Testing Exercise 

Symbiosis is a living (1) for (2) (3). It 

is a (4), sometimes between (5) and (6) as 

in the hydra and algae and sometimes between two plants as in the 

(7) and the (8) ; or between two animals as in the 

(9) (10) and (11) anemone. A (12) 

lives on another (13) organism known as a (14), 

I taking food from it but giving (15) in (16). Many 

parasites do (17), causing (18) or (19) of 

j their hosts (20) is continually combating (21). 

PROBLEM IV. HOW DOES MAN DISTURB THE BALANCE OF 

NATURE? 

Man and the balance of life. Man has come to disturb the 
balance of life in many ways. He has introduced water to regions 
1 and made them support plant and animal life some of which 
are parasites ; he has placed new plants in new localities and had 
them exterminate the native plants ; and unwittingly he has dis- 
turbed the balance which nature had established. He has brought 
into this country, insects which are doing millions of dollars of 
damage every year, witness the browntail moth and the gypsy 
moth in New England, and he is now going to the ends of the 
earth to find the natural enemies of these imported pests ; as is seen 
in the importation of the ladybird beetle from Australia to feed 
upon the imported citrus scale insects brought to California from 
Australia in 1868. He is killing off wolves and coyotes which 



290 



LIVES OF PLANTS AND ANIMALS 




U. S. Forest Service 
In places where the rainfall is sufficient we may find the ideal combination of farms and forests. 

prey upon our deer and he is protecting useful birds which prey 
upon harmful insects. Man is probably making more changes 
in life on the earth than any other living factor. But, on the 
whole, his influence is beneficial, as we will see in the units which 
follow. 

Practical Exercise 6. What is a parasite ? Give three examples other than 
those stated in the text. 

Practical Exercise 6. How could a student become a parasite in the school ? 
Explain. How might you become a parasite at home ? How can you avoid 
•this? 

Practical Exercise 7. Look up the term saprophyte. How does it differ 
from a parasite? Give examples of each in your environment, if possible. 

Self-Testing Exercise 

A (1) exists in (2) between organisms living in a 

region. Many (3) prey upon others, using them as (4) 

and thus holding them in check. Man has often (5) this balance 

by (6) new (7) or (8). 



PROBLEM V. HOW DO THE FACTORS OF THE ENVIRONMENT 
AFFECT ECOLOGICAL RELATIONSHIPS? 

Ecology is the study of plants and animals in relation to their! 
natural surroundings. Living things can be shown to be affected 




Wright Pierce 
In a desert, we find that plants are succulent and have spines, bristles, and rigid walls. Why? 

by two general sets of. factors in their environment, forces and 
things. These forces are temperature, light, gravity, and, to a 
lesser extent, such factors as the presence or absence of winds, the 
presence or absence of electrical storms, and the pressure of the 
i atmosphere. 

The things that affect living plants and animals are natural or 
; man-made objects with which they come in contact, such as 
foods of all kinds and the presence of other living or dead plants 
and animals in the vicinity. 

Temperature. We have already observed the effect of tempera- 
ture on the growth of seedlings. We know that certain tropical 
forms of life flourish only in heated areas, and that there are plants, 
such as the lichens of the frozen tundras of the north, that will 
grow only in extreme cold. Animal life can equally well be shown 
to be dependent upon temperature conditions. One of the most 
striking examples of this was seen in 1882 when fish, abundant in 
the Gulf Stream, were found dead and dying by the millions in a 
large area off the eastern coast of the United States. This 
i catastrophe was believed to have been caused by the cold arctic 
(current being shifted by long-continued easterly and northerly 
winds, the cold water displacing that of the Gulf Stream, thus 



292 



LIVES OF PLANTS AND ANIMALS 





is s ^Kyii 


'* \")8r.^S* ^"'tf^n 








w. m-'mw-M^mi 


11 ^1 n'v 


nNI 


jjt flKj SB^"'- S/*&GsT&&w^\ 4BK* 


ii ffl ^ Sr- 


. • jh! $9 


¥$'■ Sf^SB 8* * ' 'B&M& 'S d 


ii-$-.# 


ill 


•J 5 


I-- # v T WI ' >* I 


m&mmi 






aBfP-SN^V'U-- ; .'K 




|jy 




$Tfc5*|S 


; :--,:w ; r'. J .*■■ 




jjfc'4af 


•■^ttif ■*• t: 




^^r^i-..>.>. 1 


^ ' !¥?? £j! 




• ^*.^\%|'f , : 




ait; 


?ft 


i 




■ ■-■■! rWl / 



E7. S. Fores* Service 
In the tropics, where heat and rainfall are plentiful, vegetation is abundant. Why is this true? 

causing the death of the fish. Fish breeders know how sensitive 
young fish are to changes of temperature, and any fisherman knows 
that the trout will go into deep water or will lie in the cool spring 
holes during hot weather. 

We know plants either die or become dormant in winter, while 
many animals hibernate (become inactive) during the cold 
weather. But we are not so apt to think of the effect of con- 
tinuous cold or equally continuous warmth as seen in the arctic 
regions or in the tropics. The wealth of tropical vegetation and 
animal life is due in part to the higher temperature. Animals 
develop faster and go more quickly through their life cycle. In 
southern California the heat often transforms garden biennials 
into annuals and the converse is seen in cold countries where 
annuals may be changed for a time to biennials. High temperature 
seems to increase the amount of certain pigment in birds and other 
animals so that they are more highly colored in hot climates. 

On the other hand, some fish, as the trout and salmon, are 
found only in cold water. Dr. H. B. Ward of the University of 
Illinois says that when salmon ascend a stream to lay their eggs 
they will invariably take the cooler branch of the river. In 
ascending the side of a mountain we find different types of animals 



LIGHT 



293 




Am. Mus. Natural Hist. 
Mosses, lichens, and dwarf shrubs are the only vegetation found in the arctic region, 

(tundra zone) . 

and plants at different elevations, the determining factor being 
largely differences in temperature. Animals normally living in 
the tropics, if brought to this country, may live, but rarely repro- 
duce. In such cases all the environmental factors except that of 
temperature are the same. 

Light. It is easy to pick examples of the effect of light on green 
plants. For example, we have the turning movements of leaves 
| and stems, the shape and color of plant leaves, and the presence or 
' absence of plants in a given region. But only recently has it been 
discovered that the flowering of certain plants depends on a lack, 
: rather than an abundance, of sunlight. Such is the chrysan- 
i themum, which flowers when the days become shorter. 

Plants and animals are sometimes grouped according to the in- 
i tensity of light in the environment. Their activity depends upon 
light, as is seen in the comparative activity of bees on a sunny and 
: on a dark day, or the activity at night of some nocturnal animals, 
as the owl or coyote. Green plants are tremendously changed if 
kept in an environment lacking in light. Compare the sprouts 
of a potato kept in darkness with one grown in the light. 

Examples of light affecting animals are many. We know that 
many animals respond negatively to strong light, as owls, bats, 

H. BIO — 20 



294 LIVES OF PLANTS AND ANIMALS 

and worms. Many animals that prey on other animals are noc= 
turnal in their habits. On the other hand, most animals can 
be shown by experiment to respond to light by definite turning 
movements. The well-known flight of the moth to death in the 
flame of a candle is an example. Experiments on the tropisms of 
insects show that a mechanical turning to the source of light is a 
very general reaction made by all insects. 

Gravity. The roots of plants respond positively to gravity by 
growing toward the center of the earth, while the stems respond 
negatively by growing away from the center of the earth. If a 
plant stem which usually grows erect is placed in a horizontal 
position, it will soon erect itself. This response is readily seen in 
trees and grasses which have been beaten down by wind and rain. 

If boxes containing germinating seeds are fixed on the rim of a 
horizontally placed wheel which is rotated rapidly, a force stronger 
than gravity is introduced and the growing stems will tend to grow 
toward the center of the wheel and the roots will grow toward the 
circumference. 

Water. We need only to look at the luxuriant growth of plants 
along a stream or irrigation ditch to realize the part water plays 
in plant life. To anyone who has visited the Imperial Valley of 
California, where water has made the desert " blossom as the rose," 
the role of water is evident. But an oversupply of water kills plants, 
as we can see along the shores of any artificial lake where the trees 
standing in the water are killed. The drying up of lakes has been 
responsible for the extermination of many fish, just as the bringing 
of water to new localities may mean new animal life in that locality. 

We have seen in the balanced aquarium some of the adaptations 
necessary for life there. Plants which live entirely in the water 
often have slender parts with finely divided leaves. Their roots 
are apt to be short and stout. The interior of such a plant is made 
up of spongy tissues which allow the air dissolved in the water to 
reach all parts of the plant. If the plant has floating leaves, as in 
the pond lily, the stomata are all in the upper side of the leaf. 

Animal life is also restricted to those forms which can easily | 
move, feed, and breathe in water. In the case of insect larvae, 
as the mosquito, we often find adaptations which enable them to 



WATER 



295 



get oxygen from the air or, as in other larvae, by gills from the water. 
Animals living in water are often shaped for living under stones. 
They are frequently protected from their enemies by having the 
same color or appearance as the bottom of the sea. They always 
have devices for catching their food, as evident in the mouth parts 
of the crayfish, or cilia in unicellular animals which sweep food in 
a water current. The tiny microscopic animals and plants, called 
collectively the plankton, which serve as food for other animals, are 




Wright Pierce 

On the left side of the illustration, we see only the type of vegetation that is charac- 
teristic of the desert, while on the right, where the land has been well irrigated, a grove of 
orange trees produces an abundant yield of fruit. 



found only in the upper levels of the water, because light penetrates 
only a few feet and the oxygen supply is deficient at greater depths. 
Sunlight heats the water rather uniformly to a depth of 30 to 
50 feet in small bodies of water and to a greater depth in the ocean, 
due to the stirring up of the surface water by wind. Great depths 
have very low temperatures. Life there is naturally much re- 
stricted and few living things are found. There are some fishes 
living at great ocean depths which are adapted to withstand the 
great pressure of the tons of water pressing in upon them. How- 
ever, we know very little about their internal structure because they 



296 



LIVES OF PLANTS AND ANIMALS 



burst when brought to the surface where the pressure is so much 
less. Few forms of life have adaptations which enable them to 
get along with the shortage of oxygen at greater depths. 




The muskrats make their homes of sticks, mud, and grass in the banks or water of streams, 
ponds, and lakes. They feed on fresh water clams and lily roots which they get from the bot- 
tom of the stream. They usually swim under water, rising only now and then to get air. 

Plants growing in dry or desert conditions, as cactus, sagebrush, 
and aloe, show a leaf surface invariably reduced, sometimes in the 
form of spines, as in the cactus. The stem may be thickened to 
store water and a covering of hairs or some other material may be 
present to lessen the loss of moisture by evaporation. If the 
water or saturated soil, in which the plant lives, contains salts, 
such as sea salt or the alkali salts of some of our western lakes, 
plants living there show many characteristics which those in desert 
conditions show. 

Animals living under such conditions are usually few and | 
restricted to those that can burrow to depths so that they may ; 
escape the heat, or lizards and snakes which are able to escape the | 
heat by taking shelter under rocks. All forms of animal life found 
there are able to live on small quantities of water. The desert 



VARYING FACTORS 297 

kangaroo rat comes out at night and burrows deep in the sand 
during the day. One of the ground squirrels avoids the hot sun 
by running from one bush to another to get shade. Both of these 
animals die if exposed to the sun for any length of time. 

Practical Exercise 8. Make a list of all the plants in your locality that are 
dependent upon a large supply of water ; those which can exist with a very 
small amount of water. 

Soil conditions. Plants grow only in soils to which they are 
adapted. Some plants, as the blueberry, require acid soils, while 
others are killed by acid in the soil. The liming of soils is one 
example of how the farmer keeps the soil in condition for the crops 
he is growing. The type of soil also affects the animals living in 
them. Mud, sand, or clay will each contain different species and 
numbers of plants or animals. Earthworms, for example, are not 
found living in acid soils. 

Food conditions. For both plants and animals food is a factor 
which determines the presence or absence of life. Mineral matter 
is so necessary for the growth of plants that manure or artificial 
fertilizer is employed to fill the need where the element nitrogen 
is lacking. The presence of animal life in water is often dependent 
upon the presence of plankton or minute forms of plant and 
animal life which live near the surface of larger bodies of water. 
Chemical substances necessary for plants and animals often de- 
termine where they will live. 

Varying factors. Other factors, such as strong winds, electricity 
in the atmosphere, the pressure of the air at different altitudes, and 
the presence of dust or chemical fumes in the atmosphere, may all 
play decided parts in determining what living things may exist in 
given localities. 

Practical Exercise 9. List all the factors of the environment that affect 
your daily life and give an example of how each one affects you. How does 
water affect the life in your community? What effect has temperature on 
plants in your locality ? Do you know any places near your home where un- 
favorable factors in the environment prevent life? Are such factors forces 
or things? Explain. 

Practical Exercise 10. Make a table naming all the factors of the environ- 
ment which affect plants and animals and show how each factor affects both 
plants and animals. 

Practical Exercise 11. From reference books, obtain a list of plants and 
animals adapted to live under conditions lacking water ; on alkali plains ; in 



298 LIVES OF PLANTS AND ANIMALS 

salt water; in a fresh-water lake. What adaptations would the plants and 
animals in the above list show? (Read Jordan and Kellogg, Animal Life, or 
Kinsey's Introduction to Biology.) 

Self-Testing Exercise 

(1) (2) are affected by the factors of the 

(3), such as (4), (5), (6), and (7). 

Plants living in water have (8) tissues which hold (9) 

and are apt to have (10) leaves and (11) roots. 

Animals living in water show (12) for such life. The 

(13) of the water is of much importance to the (14) or 

(15) living in it. At great depths it is very (16). Lack of 

water results in adaptations in plants for (17) (18) 

such as (19) or (20) or (21) stems. 

Desert animals can get along without much water, but they 

(22) in the ground or keep in the (23) much of the time. 

Temperature is a very important (24) in determining not 

only the (25) and (26) found in a given (27) 

but also how they will (28). Animals and plants 

(29) (30) in hot areas, as witness the changing of garden 

(31) into (32) in southern California. Many fish, 

as trout or salmon, are only found in (33) water. Some 

animals can only live in water containing certain (34). 

Plants and animals may be influenced not only by the (35) 

but also by the (36) of light. 



PROBLEM VI. WHY DO PLANTS AND ANIMALS FORM 
COMMUNITIES? 

Societies. All of the factors referred to act upon the plants we 
find living together in a forest, a sunny meadow, along a roadside, 
or at the edge of a pond. Any one familiar with the country 
knows that we find certain plants, and only those plants, living 
together under certain conditions, and, in a similar way, only 
certain animals will be found to be associated together. 

Plants and animals associated under similar conditions, as those 
of a forest, meadow, or swamp, are said to make up an association 
or community. If we investigate such an association, we find it 
to be made up of certain dominant species of plants ; that here and 



SOCIETIES 



299 



there definite communities exist, made up of groups of the same 
kind of plants, while certain animals will be found living on the 
plants or among them. Evidently conditions of food and shelter 
are responsible for this close association. We can see that each 
one of these plant groups in the community evidently came 
originally from a single individual which flourished under the 
peculiar conditions of soil, water, light, etc., that were found in 
this spot. These single plants have evidently given rise to like 
plants which made up a family group, and thus have popu- 
lated the locality. This is often seen in a pine grove, or in an 




Wright Pierce 
A plant society. Can you name the various plants that are living together in this group? 
What conditions and adaptations make it possible for them to live together in one society? 

area covered almost exclusively with ferns. Later, seeds of other 

plants may be carried there by the wind, birds, or other animals, 
I and we find widely different plants living under similar conditions. 
I They all need the same substances from the air, the water, and the 

soil. They all need sunlight ; they use the same food. Therefore 

there must be competition among them, especially between those 
s near to each other. The plants which are strongest and best 

fitted to get what they need from their surroundings, live ; the 

weaker ones are crowded out and die. 
But their lives are not all competition. The dead plants and 

animals give nitrogenous material to the living ones, from which 
| the latter make living matter ; some bacteria provide certain of 
\ the green plants with nitrogen; many of the green plants make 



300 LIVES OF PLANTS AND ANIMALS 

food for other plants lacking chloroplr^ll, while some algae and 
fungi actually live together in such a way as to be of mutual benefit 
to each other. The larger plants may shelter the smaller ones, 
protecting them from wind and storm, while the trees provide 
humus which holds the moisture in the ground, giving it off slowly 
to other plants. Animals scatter seeds far and wide, and man may 
even start entire colonies in new localities. 

Practical Exercise 12. Describe some plant or animal community you 
have seen. What forms of life are associated together? 

Could you have a plant community in the laboratory or school yard ? What 
conditions would you expect to find? What plants Living together? 

Self-Testixg Exercise 

Conditions of (1) (2) (3) and 

(4) are the chief factors which (5) what plants and animals 

will live together in (6). Life in such (7) is not 

all (8) but a mutual give and take. The animals and plants 

best (9) to live under such (10) crowd out the 

(11). 



PROBLEM VII. WHAT IS AN ECOLOGICAL SUCCESSION? 

Changes in environment cause changes in life. Changes are 
always taking place in plant and animal communities. Some- 
times these changes are brought about artificially, as when a forest 
fire sweeps a country or man introduces water by irrigation into a 
desert region. But always there are changes going on, which 
cause plant and animal associations to change in a given locality 
and often to move to new localities. Most of these changes are 
very slow, so that we rarely notice them. Here is an example 
quoted by Elton : A hole in a beech tree was first used by an owl 
as a nest ; then with the growth of the tree the hole became 
smaller and was used by starlings. Later it became too small for 
them to enter, and the hollow was filled by a wasps' nest. 

How plants invade new areas. New areas are tenanted by 
plants in a similar manner. Alter the burning over of a forest, 
we find a new generation of plants springing up, often quite unlike 
the former occupants of the soil. First come the fireweed and 



HOW ANIMALS GET IN NEW AREAS 



301 



other light-loving weeds, brought by means of their wind-blown 
seeds. With these are found patches of berries, the seeds of which 
were brought by birds or other animals. A little later, quick- 
growing trees having seeds easily carried for some distance by the 
wind, like the aspen, or seeds often distributed by birds, as the wild 

j cherry, invade the territory. 

I Eventually we may have the 

I area retenanted by the same 

I kind of inhabitants as formerly, 

i especially if the destruction of 

j the original forest was not 

I complete. 

In like manner, on the 

! upper mountain meadows or 
by the sand dunes of the sea- 

■ shore, wherever plants place 

I their outposts, the advance is 
made from some thickly in- 

: habited area, and this advance 
is always aided or hindered 

I by agencies outside of the 
plant — the wind, the soil, 
water, or animals. Thus the 
seeds obtain a foothold in new 
territory, and new lands are 
captured, held, and lost again 
by the plant communities. 

How animals get a foothold 
in new areas. There are 

many ways in which animals spread over new areas. Transporta- 
tion to quite distant parts may take place, as when polar bears or 
seals are carried on ice floes long distances or when insects and 
other small forms like crustaceans and snails may be carried 
hundreds of miles by ocean currents. Birds may carry encysted 
microscopic forms or even the eggs of mollusks or crustaceans in 
little balls of mud which stick between their toes. Man himself 
may play a very important part in the distribution of animals in 




Frank M. Wheat 

In the giant cactus, woodpeckers drill their 
nesting holes. In following years, these holes 
are often used as nests in turn by small owls (elf 
owls), sparrow hawks, screech owls, fly catchers, 
and wrens. 



302 



LIVES OF PLANTS AND ANIMALS 



new countries. One of the best instances of animals having 
spread when introduced by man is the case of rabbits in Aus- 




Wrighi Pierce 



If this desert region of southern California should be thoroughly irrigated, what kind of 
plant society might succeed these Joshua trees ? 

tralia. They have now become so numerous that they are a 
serious pest. The English sparrow in America and the English 
starling in New Zealand are other examples of introductions of 
animals which have become pests because of lack of enemies to 
hold them in check. 

Practical Exercise 13. Make a list of all the new forms of life introduced 
by man into your own environment. 

Food relations. Animals are confined to certain localities, 
because a food supply is there, and may migrate to new localities 
when the food supply gives out. Overpopulation with subsequent' 
lack of food brought about great migrations of the house rat 
across Russia in 1727, which was the beginning of the occupation 
of all Europe by this species of rat. 

Food cycles exist, one animal being dependent upon another! 



FOOD RELATIONS 



303 



or on plants and moving away when the food gives out. Such a 
food chain or cycle would be seen in the warblers which eat insects 
living in trees, as plant lice and boring beetles. The warblers 
are in turn preyed upon by hawks. In the same forest there may 
be mice, whose chief food is acorns, and the mice are eaten by 
owls. This is another example of a food cycle. 

Sometimes we have a sudden invasion of an animal after food, 
| such as the locust. The 
famous plague of grass- 
hoppers in Utah in early 
pioneer days was stopped 
by a similar migration of 
gulls from the Great Salt 
Lake which came to feed on 
the grasshoppers. Thus a 
balance of life is maintained. 

Ecological successions 
have already been spoken 
of. When, for example, a 
lake area dries up, different 
animals come to occupy the 
marsh and forest land, tak- 
ing the place of the water 
forms of life. Man has 
played a very large part in 
attracting new animal forms 
into regions that he has 
irrigated or reclaimed for 
agriculture. Here are an 
entirely new set of animals 
which feed upon the intro- 
duced plants. 

Life succession in a hay 
infusion. Still another ex- 
ample of an ecological suc- 
cession may be seen in a hay infusion. If we place a wisp of 
hay or straw in a small glass jar nearly full of water, and leave 




Cliff Bray 
The people of Salt Lake City, Utah, erected this 
monument in commemoration of the service done 
by the gulls in the destruction of grasshoppers. 



304 



LIVES OF PLANTS AND ANIMALS 




bacteria of 
decay are, 
presents 




hay is infused 
i«:to N/ccter- 



break dovn 
thehqx 



it for a few days in a warm room, certain changes are seen to j 
take place in the contents of the jar ; the water after a little 
while gets cloudy and darker in color, and a scum appears on the 
surface. If some of this scum is examined under the compound 
microscope, it will be found to consist almost entirely of bacteria. 
These bacteria evidently aid in the decay which (as the un- 
pleasant odor from the jar testifies) is taking place. As we have 
learned, bacteria flourish wherever the food supply is abundant. 

The bacteria them- 
selves release this 
food from the hay by 
causing it to decay. 
After a few days 
small one-celled ani- 
mals appear which 
multiply with won- 
derful rapidity. Hay 
is dried grass, upon 
which the wind may 
have scattered some 
of these little organ- 
isms in the dust from 
dried-up pools. Ex- 
isting in a dormant 
state on the hay, 
they are awakened 
by the water to active 
life. In the water, 
too, there may have been some other living cells, plant and 
animal. 

At first the multiplication of the tiny animals within the hay 
infusion is extremely rapid ; there is food in abundance and near 
at hand. After a few days more, however, several kinds of one-; 
celled animals may appear, some of which prey upon others.! 
Consequently a struggle for life begins, which becomes more and| 
more intense as the food from the hay is used up. Eventually! 
the end comes for all animals unless some green plants obtain a 



water evaporates 
animals form 
spores on 
Yuxy 





tiny animals 

arise from 
spor-ds 



larger animals appear 
and. use the 
foodt 



The development of life in a hay infusion. How can you 
account for the bacteria that attacked the hay ? 



EFFECT OF BARRIERS ON PLANT LIFE 305 

foothold within the jar. If such a thing happens, food will be 
manufactured within their bodies, a new food supply arises for the 
animals within the jar, and a balance of life results. 

Practical Exercise 14. Look for examples of ecological succession in your 
llaboratory. Any evidences of this ? Where ? 

Visit a burned-over area and note the new plants which come up. How 
Ido they differ from the old ones? 

Might a garden show examples of ecological succession? Give examples. 

Self-Testing Exercise 

(1) are always taking place in animal and plant (2). 

iNew (3) invade areas which have been (4) 

I (5), or animals (6) or shift their (7) 

because of lack of (8) or other causes. Such a change is 

[called an (9) (10). 

PROBLEM VHI. WHAT DO WE MEAN BY GEOGRAPHIC 
DISTRIBUTION OF LIVING THINGS? 

Range of plants and animals. Plants and animals inhabiting a 
given territory or area are called the flora or fauna of that range or 
area. We find out the range of a given form by collecting it in 
as many places as possible. This kind of work is interesting to 
boys and girls because they can determine the range of certain 
plants and animals in their own locality. 

The areas in which given species of plants or animals are found 
may be very limited or very wide. Some trees, for example, the 
western redwood, have a rather limited range in the extreme north- 
west while the western yellow pine or the eastern hemlock has a 
much wider range. Some of these areas were much larger in 
ancient geological times than they are now. That certain areas 
have become discontinuous is seen in the distribution of elephants, 
which once were found over a large part of the earth's surface. 
Man may reduce or increase the range of an animal, as when he 
nearly exterminated the buffalo, or introduced a pest such as the 
orange scale in California or the gypsy moth in Massachusetts 
or the chestnut canker on Long Island. 

Barriers and their effect on plant and animal life. Any one who 
has seen the Sierra Nevada mountains and knows the difference 




306 






LIFE ZONES 



307 



in life on the western and eastern slopes can tell what effect a 
mountain may have in the distribution of a given kind of plant 
or animal. Living things on one side of that range are quite 
different from those on the other. Natural barriers may be 
mountains, deserts, large bodies of water, and even rivers. Climatic 
conditions, especially, limit the range of plants, which cannot 
endure great differences in rainfall, in temperature, humidity, 
wind, or sudden atmospheric changes. Some plants and animals 
have special adaptations which enable them to cover large areas, 
such as parachutes on seeds 
and the wings of birds. For 
such plants and animals the 
geographic range will be 
greater than for less favored 
forms. 

Life zones. Reference has 
already been made to the 
fact that a zonal distribu- 
tion of plants and animals is 
easily seen in climbing any 
high mountain. Any area 
in which most of the plants 

Or animals belong tO Single Zonal distribution of plants on a mountain 
, , . , „ „ rising from a desert in Arizona. Give cause for 

Or relatively tew groups Of different zones. 

plants and animals is called a 

life zone. Life zones are often rather sharply marked, but usually 
show transitional areas between them. A region which has been 
carefully studied and which shows this zonal distribution in a 
marked way is the San Francisco mountain region in north 
Arizona. Here a mountain nearly 13,000 feet in height rises 
out of a desert plain. This mountain shows successively two types 
of desert zone, a lower and upper, each with its own desert fauna 
and flora, cactuses, sagebrush, a few birds, mice, lizards, and snakes. 
Then a' region at between 6000 and 7000 feet of pinon pines and red 
cedars, inhabited by more birds and a few mammals. Between 
7000 and 8200 feet we find forests of Douglas and balsam fir, with 
such mammals as meadow mice, chipmunks, deer, lynx, and puma. 




308 



LIVES OF PLANTS AND ANIMALS: 




Wr^^/XVZZ&ZVZlZX 



Distribution of animals on the continents. How do you account for the fact 

Where and why do you 

Higher still, between 8200 and 9500 feet, we find a typical Canadian 
vegetation, timber pine, Douglas and balsam fir and aspens, while 
the woodchuck, porcupine, rabbit, marten, fox, wolf, and other 
northern forms are found. From 9500 to 11,500 feet we find a 
fauna and flora almost like that of northern Canada and called 
Hudsonia. Stunted spruce and pine exist up to the timber fine with 
a few typical mountain mammals such as the marmot and pika or 
mountain hare. Above this area lies the rocky Alpine zone, snow- 
clad for one half of the year even in this warm, sunny climate. 
Lichens on the rocks and a few low herbs are the only plant life 
visible, while a few insects and an occasional mammal of the 
Hudsonian zone are the only signs of animal life. 

Ecological realms. The facts that the ecologist has found out 
concerning life zones have been put to practical use by the Biological 
Survey of the United States Department of Agriculture. A life 
zone map has been prepared so that the settler going into a new 
region will know at once the kind of plants and animals best 
adapted to live there. In addition, the character of the soil, the 



ECOLOGICAL REALMS 



309 




that some of the same animals are found in both North America and Eurasia? 
find other similarities ? 






rainfall, temperature range, and lists of the particular cereals, 
fruits, and vegetables that can grow in the region are made 
available to the farmer. 

Different parts of the world, each with its several life zones, are 
known as realms or regions. Australia has long been set aside as 
a distinct realm because its peculiar fauna and flora differ from 
those in other parts of the earth. North America, South America, 
the Arctic, the Antarctic, Oriental Africa, Eurasia, and Australia 
constitute the world realms. Each of these regions has animals 
and plants peculiar to itself, although resemblances are often found 
in their inhabitants. The Eurasian fauna and flora resemble 
closely those of North America. This is thought by geologists to 
mean that in former times these regions were connected by land. 



Self-Testing Exercise 

Areas inhabited by certain (1) and (2) may be 

very (3) or very (4). Barriers that affect the range 

of plants and animals may be (5), (6), and (7). 

H- BIO — 21 



310 LIVES OF PLANTS AND ANIMALS 

A mountain near a desert may show (8) (9) . Each 

of these (10) has (11) and (12) peculiar 

to itself. 

Review Summary 

Test your knowledge of the unit by : (1) rechecking on all the survey ques- 
tions ; (2) performing all assigned exercises ; (3) checking with your teacher all 
tests and doing over the parts you missed ; (4) making an outline of the unit 
for your notebook. 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = number of right answers X 3f . 

I. The balance of life (1) means that living plants and animals are 
mutually dependent upon each other ; (2) is shown by a poor garden 
crop in a dry year ; (3) in a certain region is often disturbed by man 
when he cultivates wild areas ; (4) is shown in a balanced aquarium ; 
(5) was disturbed in Australia by the introduction of water cress. 

II. The grouping of plants and animals in associations (6) is due 
to the kind of food available; (7) is called a habitat; (8) differs 
according to the environment; (9) is seen in a balanced aquarium; 
(10) is brought about by the ability of certain living things to live 
together under certain conditions. 

III. Plants and animals may be prevented from living in certain 
localities by (11) too much light ; (12) lack of certain salts in the soil ; 
(13) lack of water; (14) too much water; (15) lack of oxygen. 

IV. Symbiosis (16) is the process of living together for mutual 
advantage ; (17) is a partnership between two living things ; (18) occur 
when green plants give food to animals and depend upon certain wastes 
from them in order to make this food ; (19) is a bad thing, because it 
is a one-sided relationship ; (20) is the same as parasitism. 

V. Ecological succession (21) occurs when changes in environment 
cause changes in forms of plants and animals living in a given place; 
(22) is never brought about by man; (23) is often caused by man; 

(24) is often caused by immigrations of animals due to lack of food ; 

(25) results in new forms being found in a given locality. 

VI. Life zones (26) are found on the sides of a high mountain 
where life forms characteristic of the tropics to the arctic may be found 
from the base to the summit ; (27) are illustrated by the temperate 
zone, the torrid zone, etc. ; (28) are usually well marked but show 



TESTS 311 

transitional areas between them ; (29) are areas in which most of the 
plants or animals found belong to single or relatively few animal or 
plant groups ; (30) are not usually sharply marked. 

Achievement Test 

1. How many animal or plant societies have you found in your 
locality ? 

2. How would you stock an aquarium and keep it balanced ? 

3. How can you illustrate the nitrogen, carbon, and oxygen cycles? 

4. What are all the factors of the environment which affect living 
things in your own environment ? 

5. What is the meaning of symbiosis, and can you give exam- 
ples? 

6. Have you any local parasites and how are they controlled ? 

7. What is the effect of water upon the life in your region? 

8. How has man controlled or changed life by use of water? 

9. What geographic region do you live in and what are the chief 
characteristics of its flora and fauna ? 

Practical Problems 

1. Select some locality near you and try to work out the animal 
and plant communities there. 

2. Make a map for your notebook, showing zonal distribution of 
plants and animals for your locality. 

3. Take an area in your own yard one foot square and list all the 
living things you can find there. 

Useful References 

Coulter, Barnes, and Cowles, Textbook of Botany, Vol. Three. 

(American Book Company.) 
Downing, Our hiving World. (Longmans, Green & Co. 1924.) 
Elton, Animal Ecology. (The Macmillan Co. 1927.) 
Flattely and Walton, The Biology of the Sea Shore. (The Macmillan 

Co. 1922.) 
Howes, Insect Behavior. (R. C. Badger.) 
Jordon and Kellogg, Animal Life. (D. Appleton & Co.) 
Loeb, Forced Movements, Tropisms and Animal Conduct. (J. B. 

Lippincott Co. 1918.) 
Needham, General Biology. (Comstock Publishing Co.) 
Pearse, Animal Ecology. (McGraw Hill Co. 1926.) 
Schimper, Plant Geography. (Oxford University Press.) 
Shull, Principles of Animal Biology. (McGraw Hill Co. 1924.) 




SURVEY QUESTIONS 

Have you ever seen an interscholastic track meet and noticed the 
different ways in which the athletes use their muscles ? Why must the 
members of a football team train ? Do you know why we have a skeleton ? 
Can you give the uses of the skin ? Do you know what constitutes good 
posture? Do you know what are the most sensible kinds of shoes? 



Wide World PTwto 



312 



PART IV. THE BIOLOGY OF MAN 

UNIT X 
HOW DOES THE HUMAN MACHINE DO ITS WORK? 

Preview. I suppose every boy and girl who reads these pages 
has seen an interscholastic track meet and perhaps envied the 
perfect coordination of every part of the bodies of the men who 
run hurdles, high jump, or pole vault. Perhaps you have tried 
some of these feats yourself and have discovered how difficult it 
is to make the different muscles coordinate at exactly the right 
time. It is a very wonderful machine, this body of ours, and we 
cannot help but feel a real reverence for it when we think of the 
delicate mechanism which, with its numerous adjustments and 
adaptations, can do work so efficiently. Unl ik e a man-made 
machine, the body is seK-directed, and with care will far outlast 
most machines made of iron and steel. 

In all animals, and the human organism is no exception, the body 
has been likened to a machine in that it turns over the latent or 
potential energy stored up in food into kinetic energy f mechanical 
work and heat), which is manifested when we perform work. One 
great difference exists between an engine and the human body. 
The engine uses fuel unlike the substance out of which it is made. 
The human body, on the other hand, uses for fuel the same sub- 
stances as those out of which it is formed; it may, indeed, use 
part of its own substance for fuel. The human organism does 
more than purely mechanical work. It is so delicately adjusted 
to its surroundings that it will react promptly and efficiently to 
stimuli from without ; it is able to utilize its fuel (food) in the most 
economical manner ; it is fitted with machinery for transforming 
the energy received from food into various kinds of work; it 

313 



314 HOW DOES THE HUMAN MACHINE DO ITS WORK? 

provides the machine properly with oxygen so that the fuel will 
be oxidized; and the products of oxidation are carried away, as 
well as other waste materials which might harm the effectiveness 
of the machine. Most important of all, the human machine is 
able to repair itself. 

No boy or girl can go into the big game of life and expect to be 
a helpful member of society with an insufficient knowledge of the 
human machine. Neglect or lack of proper care of our bodies may 
defeat some of our life's fondest ambitions. The efficient citizen 
should be the healthy citizen. 

PROBLEM I. WHAT IS THE GENERAL STRUCTURE OF THE 
HUMAN BODY? 

Laboratory Exercise. The structure of the human body. Use 

manikin or good chart. 

Note the covering of skin. Can you think of any uses for this 
structure? What general uses would the muscles have? Note their 
position with reference to the skeleton and the organs of the body 
cavity. Take off the covering and examine the organs within the 
body cavity. The thin layer of muscles that separates the heart and 
lungs from the abdominal cavity is the diaphragm. Use a good text 
figure to locate the parts of the digestive tract : stomach, small and 
large intestines, liver, and pancreas. Locate the kidneys, and the 
tubes (ureters) leading to the bladder and thence outside of the body. 

Skin and muscles. If we are thinking of the body as a machine 
which does work, then it is obvious that, while the skin is partly a 
protective organ, the muscles are structures by which work is largely 
accomplished. The diagram (p. 320) shows that they are attached 
to bones which serve as levers and thus accomplish movement. 

Other body structures. In spaces between the muscles are 
found various other structures — blood vessels, which carry blood 
to and from the great pumping station, the heart; connective 
tissue, which holds groups of muscle or other cells together; fat 
cells, scattered in various parts of the body ; various gland cells, 
which manufacture the enzymes which digest our foods ; and the 
cells of the nervous system, which aid in directing the various 
parts of the body. 

Body cavity. Within the cover of skin, bone, and muscle is a 
cavity filled with various organs. A thin wall of muscle called 



THE NERVOUS SYSTEM 315 

the diaphragm (di'd-fram) divides the body cavity into two unequal 
cavities. In the upper one, thoracic cavity, are found the heart, 
lungs, and esophagus; in the lower, the abdominal cavity, are the 
stomach, intestines, the liver, the kidneys, and other structures. 

Digestion and excretion. The mouth cavity leads into a food 
tube into which food passes and from which digested or liquid 
food is absorbed into the blood to be carried to the cells of the 
various organs which do the work. Emptying into this food tube 
are various groups of gland cells, which pour digestive fluids over 
the solid foods, thus aiding in changing them to a soluble form. 
Solid waste materials are passed out through the posterior end of 
the food tube, while liquid wastes are eventually excreted by means 
of the skin and of organs called kidneys. 

The nervous system. This complex machine is much more 
than a mechanical engine. It is self-directed. All its functions 
are either directly or indirectly under its control. Not only are 
animals able to receive outside stimuli through certain parts called 
sense organs, but they react to them, and there is internal co- 
ordination and control as well. The complicated machine does 
its work automatically; the heart beats, the glands secrete, the 
chest rises and falls without any conscious direction on our part. 
The nervous system gives sensation, it gives internal control and 
coordination. In man it does more. It also gives him control 
over his conscious activities. He is able to make a selection or 
choice of his daily acts. As such he is a " thinking " animal and 
has become master of the earth. 

Practical Exercise 1. Make in tabular form for your workbook a summary 
of work done by the different parts of the body. 

Self-Testing Exekcise 

Check in your workbook the statements that are true. 

T. F. 1. The human body is like a machine because it can repair 
itself. 

T. F. " 2. Food is oxidized in the human body as is fuel in an engine. 

T. F. 3. The skin is an organ of protection but not of excretion. 

T. F. 4. The nervous system gives sensation as well as body control. 

T. F. 5. Movement is accomplished in the body because muscles 
are attached to bones which act as levers. 



316 HOW DOES THE HUMAN MACHINE DO ITS WORK? 

PROBLEM n. WHAT IS THE STRUCTURE OF THE SKIN? 

Laboratory Exercise. To find out some functions of the skin. 

Hand lens. Ether or alcohol. Large glass jar. Two thermometers. 
Model or illustration showing section of skin. 

Find out whether all parts of the skin of the arm are equally sensi- 
tive, by touching various parts of it with the sharp point of a pencil. 
Cool a large glass jar, and hold the hand and wrist in the jar for a few 
moments, closing the opening of the jar with a cloth or a towel. What 
collects on the inner surface of the jar? 

What happens when you take violent exercise? Weigh yourself 
before and after a period of hard work in the gymnasium. Is there 
any loss in weight ? How do you account for it ? 

Place a few drops of ether or alcohol on the back of your hand and 
note the evaporation of the liquid. What sensation do you feel while 
the evaporation takes place? 

Study the model or diagram of skin on page 17. Locate the two 
layers. Find and describe the sweat glands, oil glands, and sense 
organs. Draw a diagrammatic sketch of the model and label all 
parts. Write a statement giving the functions of each part. 

Conclusions. Is the skin an organ of sensation? What passes off 
through the skin? What effect on your bodily comfort does this last 
function have? 

The skin. Covering the body „is the protective structure 
called the skin. Under the epidermis, a layer of dead cells, there 
are delicate sense organs, lying in the dermis or true skin, which 
give us sensations of touch, pressure, and temperature. The skin 
aids also in passing wastes out of the body by means of sweat 
glands, and it plays an important part in equalizing the tempera- 
ture of the body. 

Nails and hair. Nails are outgrowths of the horny layer of the 
epidermis. A hair is also a growth of the epidermal layer, although 
it is formed in a deep pit or depression in the dermis ; this pit is 
called the hair follicle. 

The glands of the skin. Scattered through the dermis, and 
usually connected with the hair follicles, are tiny oil-secreting 
glands, the sebaceous (se-ba'shus) glands. The secretion of these 
glands keeps the hair and surface of the skin soft and. pliable. 
The other glands in the dermis, known as sweat glands, are to be 
found in profusion, over 2,500,000 being present in the skin of a 
normal man. These glands excrete certain wastes from the blood 
in the water they pass off. 



SKIN INFECTIONS AND THEIR CARE 



317 



The skin is first of all an organ of protection against man's 
microscopic foes, the bacteria. But a dirty skin harbors bacteria. 
Moreover, the skin 
pores, through which 
the perspiration and 
oil pass, are easily 
clogged with dirt. 
Frequent washing is 
necessary if we wish 
to keep the skin 
clean. Pride in one's 
own appearance for- 
bids a dirty skin. 
Powder or rouge does 
not clean the skin; 
it may cover up dirt. 




nsory-~, ^ £ 

nerve to IV 

VeS5e3f7*g 

. nerve. ; 3 d 
to sveot -j 2. 



>s f at cells 



SLcbcucto-Treocc^ 

area 

For those Who Can A section through the skin. What are the uses of the various 

stand it, a cold 

shower or sponge bath should be taken every day with a brisk rub- 
down afterward, since this exercises the blood vessels of the skin. 
Soap should be used daily on surfaces exposed to dirt, because it 
combines with the oil of the skin, thus aiding in the removal of 
the dirt held there. Exercise in the open air is important to all 
who desire a good complexion. To have the " glow of health " 
one must exercise the skin, as well as keep it clean. 

Skin infections and their care. We are all aware of the fact 
that sometimes a scratch or cut becomes infected; bacteria multiply 
there and cause pus. Pimples are often caused by the infection 
in the skin pores of rod-shaped bacteria, while boils are usually 
caused by the infection of the hair follicle with pus-forming 
bacteria — the streptococci (strep-t6-k6k'sl). 

Whenever the skin is broken, it is necessary to prevent the 
entrance and growth of bacteria. This may be done by washing 
the wound with weak antiseptic solutions such as a three per cent 
carbolic acid solution, a three per cent lysol solution, or by painting 
the wounded part with solution of iodine or mercurochrome. These 
solutions should be applied immediately. A burn or scald should 



318 HOW DOES THE HUMAN MACHINE DO ITS WORK? 

be covered at once with a paste of baking soda, with olive oil, or 
with a mixture of limewater and linseed oil. These tend to lessen 
the pain by keeping out the air and reducing the inflammation. 

The relation of clothing to the skin. Clothes are primarily for 
protection. They may be classed as either good or bad conductors 
of heat. Good heat conductors, such as linen or cotton, allow the 
temperature outside of them to replace that of the layer of air 
directly around the body, while silk and wool are poor conductors 
and protect the body from a lower temperature outside. Warmth 
of clothing is largely dependent on the amount of air held between 
its fibers. Cool clothes have little air space in the meshes of the 
cloth, while loosely woven underclothes are warmer because they 
absorb perspiration rapidly and dry out quickly. Hence they 
do not feel cold or clammy to the perspiring skin as linen and 
cotton do. Young people can wear linen or cotton underclothes 
safely all the year round if they make proper changes in the weight 
of their outside garments. Older persons, on the other hand, need 
to wear woolen underclothes in the winter because these keep out 
cold and absorb perspiration without chilling the skin. 

Self-Testing Exercise 

The skin is composed of (1) layers, the (2) and 

(3), the latter is the (4) layer and is largely (5) . 

The skin excretes certain wastes through the (6) glands. An 

open wound may become infected by (7) which cause 

(8) . Boils are an example of an (9) by (10) . 

The skin is a (11) covering consisting of the epidermis, a layer 

of (12) (13), and the living (14) which con- 
tains the (15) and (16) glands, (17) 

(18), (19), and (20) (21). 

PROBLEM m. WHAT IS THE RELATION OF MUSCLES TO 

BONES? 

Laboratory Exercise. To study the use of the muscles and bones. 

Frogs preserved in formalin, mounted skeletons of frog, manikin, 
human skeleton, or good diagram. 

Note the " flesh " forming the muscle of the leg. (A muscle is 
attached to the bone by a tough tendon.) 

Holding your leg still, raise the foot up and down. Where do you 
feel the contraction of the muscle? Referring to the manikin, deter- 



BONES AND MUSCLES 



319 



mine how these muscles are attached to the bones? At how many- 
points are they attached? 

Explain how movement of the leg results from contraction (shorten- 
ing) of certain of the muscles. What must occur when some of the 
muscles contract ? (Look at the position of the muscle on the opposite 
side of the leg.) 

Note the shape of your upper arm. To what is the rounded surface 
due? Move it and watch what happens to the muscles. Now 
examine the skeleton or a diagram to see if you can make out just 
where the muscles are attached. Why do muscles cause movement? 
Explain fully. What use, other than movement, have muscles ? 

Practical Exercise 2. From a study of diagrams and skeletons of a man 
and of some other mammal, as a cat or a dog, make labeled diagrams for your 
workbook to show the position of the main parts of the skeleton, vertebral 
column, skull, shoulder and pelvic girdles, and the appendages. 

Bones and muscles. The body is built around a framework of 
bones. These bones, which are bound together by tough ligaments, 
fall naturally into two great groups : 
the bones of the trunk and head, 
namely, the vertebral column, ribs, 
breast bone, and skull, which form 
the axial (ak'si-al) skeleton; and 
the bones of the appendages (the 
framework of the arms and legs), 
which, together with the bones at- 
taching them to the axial skeleton, 
form the appendicular (ap-en-dik'ti- 
ldr) skeleton. 

To the bones are attached the 
muscles of the body. Movement 
is accomplished by the contraction 
of muscles, which are attached so 
as to cause the bones to act as 
levers. Muscles usually act in 
pairs : one muscle extends while the 
other flexes or bends. Bones also 
protect the nervous system and 
other delicate organs. The bony cranium (kra'ni-#m), inclosing 
the brain, is an example of such protection. The internal skeleton 
also gives form and rigidity to the body. 




•skccll 

.clavicle 
sternum 

..Taumems 

-vertebra 

.ulna 

.racCiurs 



What are the uses of the skeleton ? 



320 HOW DOES THE HUMAN MACHINE DO ITS WORK? 



Hygiene of muscles and bones. Young people especially need 
to know how to prevent certain defects which are largely the result 

of bad habits of posture. 
Good posture is a con- 
dition of equilibrium of 
the body which can be 
maintained for some time, 
such as standing or sitting 
erect. Standing erect is 
a good habit ; round 
shoulders are an indica- 
tion of a bad habit. The 
habit of keeping a wrong 
position of bones and mus- 
cles, once formed, is very 
hard to correct. 

Round shoulders are 
most common among peo- 
ple whose occupation 
causes them to stoop. A 
wrong position at one's 
desk is among the causes. 
Exercises which strengthen 
(&) the muscles of the back 

Muscles work in pairs — Explain what is happening to a pg helof ul in forming the 
the foot in (&). *. & 

habit of erect carriage. 
Slight curvature of the spine either backward or forward is 
helped most by exercises which tend to straighten the body, 
such as stretching up with the hands above the head. Lateral 
curvature of the spine, too often caused by a " hunched-up " 
position at the school desk, may also be corrected by exer- 
cises which tend to lengthen the spinal column. If your pos- 
ture is not good, study your own defects and find out from an 
orthopedic specialist just what you should do to correct it. 
Then go to work to correct it. Remember it takes a long 
time to overcome results of wrong posture that may have taken 
years to form. 





CARE OF THE FEET 



321 



.ear- 



Importance of good posture. It is the duty of every girl and 
boy to have good posture and erect carriage, not only because of 
the better state of health which comes 
with it, but also because self-respect de- 
mands that we make the best of the gifts ^...skoickter- 
that nature has given us. An erect head, 
straight shoulders, and elastic carriage go 
far toward making their owner both liked 
and respected. The person who stands 
erect and has good posture is usually the 
one who has good mental poise as well. 



.hip 



....kraee 



Practical Exercise 3. Make an outline of 
what you would do to correct (a) flat feet, (6) a 
lateral spine curvature, (c) round shoulders, 
(d) protruding abdomen. 



.cmkl^ 



In good posture, the head is 
directly over the feet. A line 
dropped from the ear passes 
through the middle of the 
shoulder, the hip, knee, and ankle. 



Care of the feet. Our health depends 
to a large degree upon exercise. Little 
exercise is possible without the use of the feet. Most of us have 
known foot discomfort of one sort or another. Let us see how 
to avoid such difficulties. 

Many foot troubles come from either too tight or too loose 
shoes chafing the foot, thus causing the skin to respond to the 
irritation by forming callous spots which grow thicker and thicker, 
developing into corns. But a much more serious effect comes 
from the use of badly shaped shoes with high heels. If you look 
at the human skeleton, you will see that the bones of the foot form 
an arch from the toes to the heel, so that the foot, between the ball 
and the heel, should touch the ground only slightly. High-heeled 
shoes throw the weight forward to the ball of the foot, pressing the 
bones of the arch into unnatural positions and straining the ten- 
dons which fasten the muscles to the bones. The foot in a natural 
position on the ground is also seen to touch along the edges outside, 
but not in the middle of the foot. This arch is weakened by the 
use of too narrow and too pointed-toed shoes. 



Practical Exercise 4. Make an outline drawing of the sole of your shoe as 
you stand. Then make an outline of your bare foot as you stand on the first 
outline. How do the two outlines compare? Are you wearing proper shoes ? 



322 HOW DOES THE HUMAN MACHINE DO ITS WORK? 

Tight shoes, high heels, and " toeing out '" all tend to cause 
strain on the arch and consequently cause flat feet. A severe 
case produces strain known as a " broken arch," and this con- 
dition may produce severe pain or even nervous disorders. An 
orthopedic specialist should be consulted in such cases. 

Self-Testing Exercise 

The body is built around a framework of (1). These form a 

central (2) skeleton and attached portions called collectively the 

(3) skeleton. Muscles are attached to (4) which act as 

(5). Muscles usually act in (6) one (7) while 

its opposite is (8) . Good posture is necessary for good 

(9) and can only be obtained by constant (10) . Posture is a 

position of (11) of the body. Tight shoes cause (12) 

on the (13) and other foot (14). 

Review Summary 

Test your knowledge of the unit by : (1) rechecking all the survey questions ; 
(2) performing all the assigned exercises ; (3) checking with your teacher the 
scores of the various tests and doing over those that you missed ; (4) making 
an outline of the unit for your notebook. 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 4. 

I. The body may be compared with a machine because (1) it does 
work ; (2) it is made of organs ; (3) it has a self-directing mechanism ; 
(4) it oxidizes substances to release energy; (5) it provides for the 
disposition of its waste products. 

II. The skin (6) is of no value as a protection ; (7) is a heat-regulat- 
ing mechanism ; (8) protects the body against invasion from germs ; 

(9) can best be kept clean by covering with rouge or powder; 

(10) contains many pores leading from sweat glands which must be kept 
open if the skin is to function properly. 

III. The skeleton (11) is a framework to which muscles are at- 
tached ; (12) acts as a protection for the soft parts of the body ; (13) is 
made largely of lime; (14) gives shape to the body; (15) is entirely 
external in man. 



USEFUL REFERENCES 323 

IV. Muscles (16) usually work in pairs; (17) are usually attached 
to bones, which act as levers; (18) never give form to the body; 
(19) are capable of contraction and relaxation ; (20) are only fully devel- 
oped in people who exercise. 

V. Good posture (21) comes as a result of a proper balance or 
equilibrium of body parts; (22) is the result of round shoulders; 
(23) is an indication of good mental as well as physical health ; (24) is 
not necessary for health ; (25) may be obtained through proper exer- 
cise and care of the body. 

Achievement Test 

1. What is the general plan of man's body make-up? 

2. What would you do in case of a skin infection? 

3. What are the functions of each part of the skin? 

4. How could you show the ways in which the leg muscles work in 
walking? In running? In jumping? 

5. How would you protect yourself from foot troubles ? 

Practical Problems 

1. Visit a museum and make a series of diagrams for your workbook 
to show the relationship of man to the other mammals. 

2. Study diagrams and the foot of the human skeleton in order to 
locate the arches in your foot. Make an impression of the foot on 
smoked paper and decide if your arches are in good condition. What 
exercises should you take if they are not ? (See the Metropolitan Life 
Insurance pamphlet, " Foot Health.") 

3. Prove that a given bone acts as a lever for certain muscles in 
your body. 

4. What first aid would you administer for a broken bone in your 
leg? For a bad scratch made by a rusty nail? 

Useful References 

Hunter, Laboratory Problems in Civic Biology, pp. 93-96 inclusive. 

(American Book Company.) 
Kimber and Gray, Textbook of Anatomy and Physiology. Chapters 

IV-VI inclusive. (The Macmillan Co. 1926.) 
Metropolitan Life Insurance Company, Foot Health. 
Walter, Human Skeleton. (The Macmillan Co. 1918.) 
Williams, Personal Hygiene Applied. Chapter VI. (W. B. Saunders 

Co. 1925.) 




SURVEY QUESTIONS 

What are vitamins and what do they do ? Do you know why milk is a good 
food? Why do we eat so many different kinds of foods? What makes 
foods cheap or expensive ? Is it true that all cheap foods are poor foods ? 
Do you know what adulteration means ? Give an example. 



Photo by H. Armstrong Roberts 



UNIT XI 



HOW DOES MAN DETERMINE THE VALUES OF FOODS? 

Preview. Anyone reading advertisements in a magazine today 
cannot help noticing the number of food slogans that the pro- 
ducers of food place before the public. " An apple a day keeps 
the doctor away/' " Take your daily orange juice," " Eat yeast 
and get your vitamins," " Drink a quart of milk a day," etc. We 
naturally want to know just how many of these statements are 
true. The facts concerning what we should eat and why we should 
eat certain foods are certainly worth knowing. 

Every one knows that the human machine needs fuel. A 
locomotive uses coal, water, and oxygen. A living animal gets 

324 






PREVIEW 325 

food, water, and oxygen from its environment. 1 Both the non- 
living and the living machine do the same thing with fuel or food. 
They oxidize it and make use of the energy thus released. They 
both receive heat as a direct result of this oxidization or burning. 
In addition, however, the living organism may use food to repair 
parts that have broken down or even build new parts. Thus 
food may be denned as something that can be used by the 
body of a plant or animal to release energy, or to form material 
for the growth or repair of that body. However, we must not 
think of our body as taking the foods and burning them directly, 
thus providing us with heat and energy to do work. It is a much 
more complicated process than this might sound. Our digestive 
organs first have to break down the food materials into such forms 
that they can be taken into the blood and carried to all parts of 
the body. The millions of cells of which the body is composed 
must be given more material which will form new living matter. 
These cells must also be provided with food material which is 
oxidized to release energy when muscle cells move, or gland cells 
secrete, or brain cells work. 

Experiments have proved that an animal may be provided with 
what seems to be the foods necessary to burn and make tissue, 
and yet it will die. Professor Mendel of Yale and his students 
have shown that unless animals receive proteins that contain 
certain so-called amino acids they will die, although their diet 
is apparently sufficient in quantity and quality. It has been 
found that in certain proteins there are these amino acids which 
are used by the animal to build up its tissues. So important are 
these substances that the Germans have called them " building 
stones," for without them no growth can take place. Animal 
proteins appear to have more of these amino acids than do plants. 
Hence we see the value of a mixed diet which includes both plant 
and animal foods. Milk appears to have both the necessary 
amino acids and certain other substances called vitamins of which 
we shall hear more later. Certain mineral salts, as calcium, iron, 
sodium, and potassium, are also needed by the body. 

1 Animals and some plants get organic food from their environment ; but green 
plants make organic food from materials which they get from their environment. 
h. bio — 22 



326 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

We live in an age where practical applications of science are 
found at every turn. It is right that this should be so, for we are 
more and more surrounded by the things made by science and the 
things done by science. Foods, which not so many years ago were 
used directly from the stream or field, are now put through a manu- 
factured process which changes them very greatly. Sometimes 
the raw plant or animal substances are put into cans and pre- 
served for our use. It is little wonder that as food in these new 
forms began to be marketed that the unprincipled food handlers 
began to adulterate or misbrand their foods, thus cheating the 
purchaser. State government, and later the United States govern- 
ment, began to inspect such foods, and found that nearly half the 
total number of samples examined were adulterated. The Pure 
Food and Drugs Act of 1906, with its subsequent requirements, 
was the result of these investigations. At the present time, due 
to official examinations and inspection, only a very small amount 
of adulterated or misbranded food is shipped from one state to 
another. But materials manufactured and sold in the same state 
may still be adulterated, since the Pure Food and Drugs Act does 
not control this situation. 

One feature of adulteration that the Pure Food and Drugs Act 
does not cover in a very satisfactory way is the labeling of patent 
medicines. While the presence of certain habit-forming drugs 
and poisons must be shown on the label, there are scores of other 
deadly poisons that may get into medicines without appearing on 
the label at all. The labeling of patent medicines is controlled 
by the Pure Food and Drugs Act ; but the purchase of such medi- 
cines is in the hands of the American public. Uneducated people 
will not read labels very carefully, with the result that the patent 
medicine industry thrives and people throw away several hundred 
million dollars each year and do what is far worse, damage them- 
selves while they spend their good money. 

The worst situation, however, exists with reference to the use 
of alcoholic beverages. Some of the American people are being 
extremely unpatriotic, and, incidentally, are taking big chances 
with " bootleg " liquor. Dr. Louis I. Dublin, in a book entitled 
" Health and Wealth," points out that in states where the Pro- 



THE NUTRIENTS 



327 



hibition Amendment is not carried out the death rate from alco- 
holic poisoning has gone above the level of pre-prohibition days, 
while in states where prohibition is more widely enforced, the 
death rate is lower than the period before the World War. We 
should attempt to get at the truth with reference to prohibition 
and at least show ourselves good citizens by upholding the law 
whether we believe in it or not. 



PROBLEM I. WHAT DO FOODS DO FOR US? 

Practical Exercise 1. Make a list of foods that you have eaten in the last 
24 hours. By referring to tables in government bulletins or any good lab- 
oratory manual, classify the foods under the following headings. 



Nutrients 


Much 


Little 


1 
None 


Carbohydrates . . 

Proteins 

Fats 









What are the uses of foods ? If we use the simile of the human 
body and the engine, then it is obvious that body heat and the 
energy we release in our daily work comes from the foods we eat. 
But unlike an engine, which cannot repair itself if damaged, we not 
only repair injuries to our bodies but can actually increase in weight. 
Food then furnishes material for body growth, for repair of waste, 
for heat, and for work when oxidized in the cells of the body. 

The nutrients. Foods contain substances called organic 
nutrients. These we have already learned are proteins, carbo- 
hydrates, and fats or oils. Foods also contain waste. A leg of 
lamb contains bone and tendons ; oysters and clams have shells ; 
potatoes and turnips have skins ; and bananas and oranges have 
outer coverings which cannot be used. All foods have some waste. 
In addition, they contain various amounts of mineral salts and 
frequently a large amount of water. 

Proteins are nutrients which contain nitrogen in addition to 
carbon, oxygen, and hydrogen. Foods containing a high propor- 
tion of proteins are lean meats, eggs, some nuts, peas, and beans. 

Carbohydrates contain carbon, hydrogen, and oxygen, having 



328 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

the two latter elements in the proportion found in water. Foods 
rich in carbohydrates are cereals, breads, cakes, fruits, and jellies. 
Sugars are pure carbohydrates. Fats and oils contain carbon, 
hydrogen, and oxygen, but their chemical formula shows a rela- 
tively small proportion of oxygen. Examples of foods containing 
fats are butter, lard, suet, olive oil, and mayonnaise dressing. 

The fuel value of food. In various experiments it has been 
agreed that the energy stored in foods as a source of heat should 
be stated in heat units called Calories. A Calorie is the amount of 
heat required to raise the temperature of one kilogram of water one 
degree Centigrade. This is about equivalent to raising the tempera- 
ture of one pound of water four degrees Fahrenheit. The fuel 
value of different foods may be computed by burning a given 
portion of each food in a calorimeter. It has thus been found 
that a gram of fat will liberate 9.3 Calories of heat, while a gram 
of carbohydrate or protein will each liberate only about 4 Calo- 
ries. The burning value of fat is, therefore, over twice that of 
carbohydrates or proteins. 

Fats and oils have the highest energy value of all foods. But 
because of their rather indigestible qualities and because one soon 
tires of an excessive amount of fat, carbohydrates are more used to 
release energy. Cereals, bread, potatoes, and other starchy vege- 
tables should, for this reason, be a part of our daily diet. 

Tissue building and repair of waste. But it is not sufficient 
for man to " count his Calories/ ' We are made of living matter, 
protoplasm. Living cells may waste away, and need to be repaired 
or replaced. New cells must be formed. According to Rose 
it is estimated that the body of a baby at birth contains about 
4000 Calories of burnable material, while that of a full-grown man 
averages about 70,000 Calories. Where did this growth come 
from? Evidently, the tissues use food for building purposes. 

We have already seen that carbohydrates, fats, and proteins 
all contain the elements carbon, oxygen, and hydrogen, and that 
proteins alone contain the element nitrogen. We have learned 
also that the protoplasm, which forms a large part of the body, 
is thought to be a very complex compound composed of car- 
Jbon, hydrogen, oxygen, nitrogen, and ten or more other chemical 



VALUE OF PROTEIN 



329 



thermometer 
showing change- 



elements. If living matter is to grow, it must have the proper 
elements for building. And these it can obtain from food. Pro- 
teins, although they may 
be oxidized to release en- 
ergy, are usually utilized 
to give the body its nitro- 
gen, from which, in part, 
living protoplasm is manu- 
factured. 



Demonstration 1. Feed two 
white rats of equal weights 
for a period on different diet- 
aries, using in one case an 
incomplete protein (such as 
gliadin of wheat) and the 
other with a complete protein 
(such as in milk) containing 
the essential amino acids. A 
striking contrast may be ob- 
tained by feeding both with 
exactly the same foods except 
that one has a given amount 
of milk substituted for the 
same amount of water. Let 
the class watch the growth 
of the two animals and report 
on the final results. Weigh 
the rats once a week. Keep 
all conditions except that of 
food exactly the same for 
both rats. 



Not all proteins are good 
tissue builders. Recent 
feeding experiments have 
shown that not all proteins 
are capable of building tissues. 




-wetter around bomb 
weermect by burnings 
of food 

A bomb calorimeter. Explain how it works. 



It has been found that the complex 
chemical substance called protein may be broken by the chemist 
into simpler proteins called amino acids. Some of these amino acids 
are useful in tissue building, and others are not. If two rats are fed 
on diets containing different amino acids, one may thrive, while the 
other wastes away and dies. For example, gelatin is a very poor 



330 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

type of protein, because it does not contain all the amino acids 
necessary for tissue building or tissue repair. On the other hand, 




Professor Hopkins showed the value of milk as a good food. Explain his experiment and re- 
sults as given in the above diagram. 

the proteins in milk contain the amino acids necessary for growth. 
It is estimated that there are eighteen of these amino acids com- 
monly found in proteins, and that all of those essential for growth 
are found in lean meat, cheese, milk, eggs, and a few grains and 
nuts. So it happens that probably most of us, without realizing, 
have used for food the proteins containing all the essential amino 
acids. 

Vitamins. These health-regulating substances must be a part 
of every diet. We know that they occur in milk and in certain 

vegetables. We shall 
learn more about 
them in the second 
problem. 

The value of water. 
It has long been 
known that water and 
the various mineral 
salts it contains are 
essential to life. The human body, by weight, is about two thirds 
water. Over 80 per cent of the blood is water. Water is abso- 
lutely essential in passing off the wastes of the body. Water 




There are eighteen different amino acids. Where any num- 
ber of these are bound up chemically they form a protein. 



THE MINERAL REQUIREMENT 



331 



makes up a very large proportion of fresh fruits and vegetables ; 
it is also present in large proportion in milk and eggs, is less 
abundant in meats, and is lowest in dried foods and nuts. The 
amount of water in a given food is often a decided factor in its cost. 

The mineral requirement. Minerals are quite as essential to 
the body as energy foods and proteins. But it is only recently 
that scientists have learned 
how important a part is played 
by minute quantities of cer- 
tain mineral substances. For 
example, the clotting of our 
blood, without which we should 
bleed to death from the small- 
est cut, appears to depend 
largely on the presence of cal- 
cium in the blood. Lack of 
calcium and phosphorus causes 
stunted growth, soft bones, and 
defective teeth, while a lack of 
iron causes anaemia and other 
disorders. If one will com- 
pute the minerals in the diet 
served in many homes, which 
consists so largely of meat, po- 
tatoes, and white bread, he will 
easily see how lacking such foods are in the mineral essentials. 
Fruits, vegetables, milk, and eggs are the best sources of all these 
minerals. Meat contains iron, but is so lacking in calcium that a 
large number of servings would be necessary to furnish the daily 
calcium requirement. Milk is one of the most important sources 
of calcium for the body and should be included in the dietary every 
day. Other minerals are just as essential as these three, but are 
not so likely to be lacking in the diet. 

Some salts, compounds of magnesium, potassium, and phos- 
phorus, aid the body in many of its most important functions. 
The beating of the heart, the contraction of muscles, and the 
ability of the nerves to do their work appear to depend on the 



ounces in a 125 lb. person. 


calcium. 


29.6 


phosphorus 


19.9 


potassium 


6.9 


sulphur- 


4.9 


sod^ urn 


3. 


chlorine 


3. 


magnesium 


1 


iron 


.08 


iocCme 


trc*ce 


fluorine 


•t 


silicon 


•• 


trcanganese 


•• 



This diagram gives the probable amount of 
minerals found in the body of a person weighing 
123 pounds. 



332 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

presence of minute quantities of these salts in the body. Thus 
they act as regulators of bodily activity. 

Practical Exercises 2. From the charts given in any laboratory workbook, 
determine the actual percentage of nutrients in beef, potatoes, oysters, and corn 
meal. Do all foods have equal nutritive value ? 

From these charts make a table containing : 

(a) Five foods rich in protein (15 per cent or more). 

(6) Five foods rich in carbohydrates (50 per cent). 

(c) Five foods rich in fat (50 per cent or more). 

(d) Five foods having a high fuel value (1500 Calories or more per pound). 

(e) Five food substances that are over 50 per cent water. How would 
water affect the cost of food, providing you had to pay for the water? 

(/) Two foods rich in mineral salts. 

In your opinion, which of the foods given are the best tissue-building 
foods ? Remember that living matter is made up of carbon, oxygen, hydrogen, 
nitrogen, sulphur, and a minute amount of mineral salts. Which do you con- 
sider the best energy-producing foods ? Explain. 

Roughage. Certain parts of foods rich in carbohydrates, usually 
the cellulose walls of plant cells, contain indigestible material 
which is useful in stimulating the muscles in the large intestine 
and thus causing the waste matter to be thrown off regularly. 
This prevents constipation. Bran, whole wheat, fresh fruits, and 
vegetables provide the best sources of these materials. 

Flavors and condiments. Most of us are aware that flavoring 
materials such as pepper, mustard, and other condiments are not 
true foods. While flavoring extracts, meat, and vegetable flavors 
do not have food value, they are of great value in making the 
food more appetizing and increasing the secretion of gastric juice. 

What are the essentials of an adequate food supply? One 
writer has said that " an adequate food supply should include 
(1) sufficient organic nutrients in digestible form to yield the 
needed energy, (2) protein sufficient in amount and appropriate in 
kind, (3) adequate amounts and proportion of various ash con- 
stituents or inorganic foodstuffs, and (4) sufficient of each of essen- 
tial vitamins." The problems which follow will help us to find 
out just what this statement means. 

Self-Testing Exercise 

A food is anything that furnishes (1) and (2) or 

(3) up the body. Foods as purchased may contain waste, 

(4) (5), (6), and (7). The or- 



VITAMINS AND THEIR USES 333 

ganic nutrients are (8), (9) or (10), and 

(11). Proteins contain (12) (13), the 

" building stones " of the body. If a protein contains the 

(14) (15) essential for (16), it is said to be a 

(17) protein (18) are essential to a diet because 

they act as (19) of various bodily (20). 

PROBLEM n. WHAT DO VITAMINS DO FOR US? 

Laboratory Exercise. Make a list of all foods which you have eaten 
within the last 24 hours. Compare j r our list with the table on pages 336- 
337 to see if you are eating foods that give you the best sources of vitamins 

A, B, C, and D. 

Vitamins and their uses. Most wonderful of all our foods are 
the regulating substances, vitamins. While little is known of their 
chemical composition, a good deal has been learned of what 
they do, or, rather, of what effect their absence will cause. These 
health-regulating substances are known as Vitamins A, B, C, D, 
E, and G. A glance at the diagram (pag3 334) shows that vitamin A, 
soluble in fats, is found abundantly in milk, egg yolk, cod-liver oil, 
and butter, and in lesser amounts in certain vegetables. Vitamin 

B, soluble in water, is found in the outer layers of many cereals 
and fruit, in milk, and in fresh yeast. Vitamin C is found in fresh 
vegetables and in citrus fruits. Vitamin D is found in cod-liver 
oil, milk, and coconuts. Vitamin E is found in meat, lettuce, 
yellow corn, whole wheat, and milk fat. Vitamin G is found in 
milk, yeast, and some meats. Vitamins appear to be largely of 
plant origin and in many cases are destroyed or their value is 
lessened by heat, although some stand high temperatures, as in 
canned tomatoes or boiled potatoes. 

So much for what they are. Now what do they do ? Rats fed 
on a diet lacking vitamin A are stunted in growth and develop an 
eye disease called xerophthalmia, which may result in permanent 
blindness. It has been known for a great many years that if 
explorers or sailors were deprived of fresh food, they suffered from 
the disease called scurvy. During the World War more than 
one war vessel was interned in a neutral port, not because of 
the guns of enemy ships, but because the crew suffered from this 



334 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

dread disease which could only be cured by a supply of fresh 
vegetables or fruits. This deficiency disease has been found to 
be caused by a lack of vitamin C. Experiments carried on in the 
Japanese navy about 1882 showed that beriberi, a serious menace 



prevents 
beri-beri 



/protects lungs /\\«D 
cmdC prevents M\\ 
e/e disease 4T\^ 



prevents 

scurvy 



prevents g~\ f\ T% prevents 
peUccgTer fjr/fci\ |J rackets 



prevents sterility 
in, rett/5 



Why are vitamins essential to the diet ? 

to health among oriental peoples, is caused by a lack of some 
substance that is not present in the rice and fish which form the 
major part of their diet, for when milk and vegetables were added 
to the diet, beriberi disappeared. Later experiments showed that 
the lack of vitamin B caused beriberi. A lack of vitamin D has 
been found to be one of the causes of rickets, a disease of chil- 
dren, " characterized by impaired nutrition and alterations in the 
growing bones." Very interesting is the fact that rickets can be 
cured by exposing the patient to the direct rays of the sun. The 
rays that have curative value are the so-called ultra-violet. These 
rays do not pass through ordinary window glass, but will pass 
through quartz or " vita glass." More interesting still is the fact 
that certain foods (such as cottonseed oil which contains no 



THE RELATION OF DIGESTIBILITY TO DIET 335 

vitamin D) when treated with ultra-violet rays also have the power 
to cure rickets. This is thought to be due to the presence in the 
foods of a substance known as ergosterol, which becomes a powerful 
antirachitic agent upon oxidation. Ergosterol is also present in 
our skin, so when we are exposed to the ultra-violet rays of the 
sun, it is probable that vitamin D is actually produced in the skin 
and thus helps in the cure of rickets. Some investigators in the 
University of California have found that when rats are fed a diet 
lacking in certain foods, such^as wheat germ, which contain vitamin 
E, they will become sterile and will not produce young. And 
latest of all is the belief that pellagra, a dread disease in many 
parts of the South, is a deficiency disease due to lack of a vitamin 
called G. 

Self-Testing Exercise 

Among the best sources of vitamin A are (1), (2), 

(3), and (4) (5) . Among the best sources of 

vitamin B are (6), (7), and (8). Among the 

best sources of vitamin C are (9) (10), and 

(11) (12). The best source of vitamin D is (13) 

(14). Rickets may be cured by including (15) 

(16) in the diet. Scurvy is caused by lack of (17) 

(18). Beriberi is caused by lack of (19) (20). 

Lack of vitamin A causes an (21) (22) . 

PROBLEM m. WHAT IS THE RELATION OF WORK, ENVIRON- 
MENT, AGE, SEX, AND DIGESTIBILITY OF FOODS TO DIET? 

The relation of work to diet. It has been shown experimentally 
that a man doing hard, muscular work needs more food than a 
person doing light work. The exercise gives the individual a 
hearty appetite; he eats more and needs more of all kinds of 
food than a man or boy doing light work, for he needs more food 
for the extra energy release. 

The relation of environment to diet. The temperature of the 
body is maintained at 98.6° in winter as in summer, but much 
more heat is lost from the body in cold weather. Hence we need 
more heat-producing food in winter than in summer. We may 



336 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 





MINERALS 


VITAMINS 






WT. 

GRAMS 


CALOR- 
IES 


WT. 
FAT 

GRAMS 


WT. 

CARBO. 
GRAMS 


WT. 
PROT. 
GRANS 


CAL- 
CI4JW 


PHOS 
PHOR- 

us 


IRON' 


A 


B 


c 


D 


E 


BEVERAGES 






























Cocoa 


1 cup 


255 


240 


12 


24 


9.5 


XXX 


XXX 


X 


XXX 


XX 


X 






Grape Juice 


1 cup 


199 200 




50 




X 


X 


XX 


XX 


XX 


XX 






Orange Juice 


1 cup 


232 100 




25 








X 


XXX 


XX 


XXX 






BREADS 






























Coffee cake 


££f 


117 


333 


12.08 


43 


8 




X 




X 


X 








Muffins, graham 


1 large 


78 


200 


3.5 


35 


6.5 


X 


XX 


X 


X 


X 








Waffles, plain 


1 6"diam. 


26.7 100 


4 


12.5 


3.5 


X 


X 




X 


X 








Rolls, French 


1 roll u |r „ 


36.81100 


1 


20 


3 




X 




X 


X 








Ham sandwich 


1 slice 2x4x| 


39 200 


14 


13.7 


5 




X 


X 




X 








Lettuce and tomato 






























sandwich 


1 slice 2x4x| 59 


108 


6 


11 


2 


X 


X 


X 


XX X 








CAKE 






























Gingerbread 


1x1^x2* 


31 


100 


2 


18 


2 


X 


X 


X 




X 








White 


1^x2x1" 


42 


135 


5 


16 


3 


X 


X 




X 










CEREALS 






























Farina * 


% cup 


170 


100 


.5 


21 


3 




X 




X 


XX 








Oats, rolled * 


1 cup 


280.5 


100 


1.83 


16.67 


4.2 


X 


XX 


X 


X 


XX 






X 


Wheat, shredded 


1 bis. 


27.4 


100 


.49 20.59 


3.51 


X 


XX 


X 


X 


XX 






X 


CRACKERS 






























Saltines 


6 


23 


93 


3 


15 


2.4 


















Uneedas 


4 


28.4 


105 


2.3 19 


2.5 


















FATS 






























Butter 


1 Tbsp. 


13 


100 


11 




.13 








XXX 


X 




X 


X 


Olive Oil 


1 Tbsp. 


11.11 


100 


11.11 






















FRUITS 






























Apple § 


1 


212 


100 


.64 


23 


.64 






X 


X 


X 


XX 






Canteloupe § 


1 4Ji' r diam. 


510 


100 




24 


1.5 






XX 


XX 


XX 


X 






Figs, dried 


iH. large 


31 


100 




24 


1.4 


X 




XX 




X 


X 






Oranges § 


1 large 


268 


100 


.3 


23 


1.61 


X 




XX 


X 


XX 


XXX 






Peaches, fresh § 


3 med. 


290 


100 


,3 


23 


1.5 


X 


X 


X 






XX 






Prunes, stewed 


2&2T. juice 


60 


100 




24 


.5 


X 




X 




XX 








NUTS 






























Brazil nuts 


2 nuts 


15.51100 


9.5 


1 


2.5 








XX 








Peanuts, sh'l'd 




























single nuts 


20-24 


18.2;100 


7 


4.5 


4.69 


X 


X 


X 


XX 


XX 








PIES 






























Apple 


*t\ arc 


136 


300 


13.3 


42 


2.25 


X 






X 


X 








Custard 


4 arc 


118 


200 


7.2 


29.5 


4.5 


X 


X 




XX 


XX 








Lemon meringue 


3"arc 


85 


450 


13.5 


76 


5.8 




X 






X 








Raisin 


4^'arc 


85 


256 


9 


52 


2.25 


X 


X 


X 


X 


X 








EGGS 






























Plain 


\H 


67.5 


100 


7.09 




9.05 


X 


X 


X 


XXX XXX 


X 


X 


X 


FISH 






























Creamed codfish 


y 2 cup 


60 


100 


5 


5.5 


8 


X 


X 


X 


XXX 


XX 


XXX 






Mackerel, broiled 


4x2x1# 


62 


100 


5 




14 


X 


X 


X 












Salmon, canned 


li cup 


52 


100 


6 




11 


X 


X 


X 


XX 


X 












* Cooked 



§ As purchased 



VITAMINS AND THEIR USES 



337 








MINERALS 


VITAMINS 






WT. 

GRAMS 


CALOR- 
IES 


WT. 

FAT 
GRAMS 


WT. 

CARBO. 
GRAMS 


WT. 

PROT. 
GRAMS 


CAL- 
CIUM 


PHOS 

PHOR 

US 


IRON 


A 


B 


C 


D 


E 


CHEESE 






























American, pale 


Vz cube 


22.8 


100 


8 


.07 


6.5 


XX 


XX 




XX 


XX 








MEATS 






























Chicken meat 


1 med. slice 


55 


100 


5.57 




12.5 




X 


X 












Beef, round pot roast 


1 slice 


43 


88 


5 




13 




X 


X 












Steak, broiled club 


aWtf. , 


51 


100 


6.5 




10 




X 


X 












Lamb, chops, broiled 


1large2x2xll£ 


46 


100 


6.5 




10 




X 


X 












Pork, bacon 


4-5 small pes. 


14 


100 


9.5 




3 




X 


X 












Ham, boiled 


4%x4xV 


37 


100 


8 




7 




X 


X 




XX 








HamDurger 


2)i"diam.xl" 


56 


100 


5 




14 




X 


X 


X 


XX 








Frankfort 


%ofIink,3%"l. 


40 


100 


7.4 


.44 


7.8 




X 














MILK 






























Whole 


% cup 


144.5 


100 


5.8 


7 


4.7 


XXX 


XX 




XXX 


XX 


X 


X 


X 


Malted 


2 Tbsp. 


25.7 


100 


.77 


19.71 


3.57 


XX 


XX 




X 


XX 


X 


X 


X 


PUD DINGS 






























Bread pudding 


%cup 


66.8 259 


12 


8 


29 


X 


X 




X 


X 








Cup custard 


%cup 


210 


225 


9 


25 


10 


X 


X 


X 


XX 


X 






X 


SALADS 






























Combination 


Xz cup 


90 


34 


.2 


6 


2 


XX 


XXX 


XX 




XX 


XX 




XX 


Fruit 


y z cup 


87 


198 


16 


11 


2 


X 




X 


XX 


XXX 


XXX 




X 


Lettuce, French 






























dressing 


1 serv. 


78 


237 


25 


2 


.8 


XX 


XXX 


XXX 


X 


XX 


XXX 




XX 


Tomato and lettuce 


1 serv. 


149 


194 


19 


5 


2 


X 


XX 


X 


XXX 


XX 


XXX 




X 


Salad Dressings 






























French 


2 Tbsp. 


24 


133 


15 






















Mayonnaise 


1 Tbsp 


14 


100 


10 


.6 


2 




X 




X 


XX 








SOUPS 






























Consomme 


1 cup 


214 


5 




.2 


1 


















Cream of clear tomato 


1 cup 


240 


269 


19 


18 


7.5 


XX 


XX 


X 


XX 


XX 


XX 


X 


X 


Split pea 


1 cup 


260 


93 


.04 


12 


10 


X 


XX 


XX 




XX 


XX 




X 


SWEETS 






























Chocolaje fudge 


iJ^fxl" 


25.5 


97.8 


2.2 


19 


.5 


X 


X 


X 


XX 


X 








Jelly beans 


6^1 large 


28 


100 




24 


1 


















Nut bar 


2x3x1" 


62 


330 


14 


47 


4 


X 


X 


X 


X 


X 








Suckers 


ifc 


26 


100 




25 




















VEGETABLES 






























Asparagus 


5 stalks 


112 


25 


.13 


13.82 


2.07 


X 


XX 


XX 




XXX 








String beans 


1 cup 


108 


45 


.32 


7 


2.44 


XX 


XX 


XX 


XX 


XX 


X 






Cabbage, shred'd 


1 cup 


63.3 


20 


.19 


3.55 


1.01 


XX 


X 


XXX 


X 


XX 


XXX 






Corn on cob 


1 ear 6" 


130 


100 


1 


19.5 


3 


X 


X 


X 


X 


XX 








Onions 


3 or 4 med. 


205 


100 


.62 


20.33 


3.3 


X 


X 


X 




X 


XX 






Peas, canned 


^cup 


180.5 


100 


.36 


17.73 


6.52 


X 


XX 


XX 


XX 


XX 








Potatoes, plain 


1 


120 


100 


.12 


22.09 


2.64 


X 


X 


X 


X 


XX 


X 






Tomatoes, canned 


1 3 4 


442 


100 


.88 


17.70 


5.31 


X 


XX 


X 


XX 


XX 


XXX 






Sauerkraut 


3 Tbsp. heap. 


100 


16 




3 


1 


X 


XX 


X 


X 


XX 


X 







After Tables of Food Values, A.V.Bradley, Santa Barbara State Teachers College, Santa Barbara, Calif. 



338 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

use carbohydrates for this purpose, as they are economical and 
easily digested. The inhabitants of cold countries get their 
heat-producing foods largely from fats. In tropical countries 
and in hot weather a considerable amount of fresh fruit should 
be used in the diet. 

The relation of size and age to diet. Age is a factor in determin- 
ing not only the kind but also the amount of food to be used. 
Young children require a large proportion of protein in their diet 
in order to grow. They are also more active than older persons 
and so use a large amount of food as fuel in proportion to their 
weight. The body constantly increases in size and weight until 
young manhood or womanhood, and then its size and weight 
remain nearly stationary, varying with health or illness. It is 
evident that adults require food only to repair the waste of cells 
and to release energy. Elderly people need much less protein 
than do younger persons. 

The relation of sex to diet. As a rule, boys need more food 
than girls, and men than women. This seems to be due, first, to 
the more active muscular life of the man, and, second, to a layer 
of fatty tissue directly under the skin of the woman, which acts as 
an insulating layer against loss of heat from the body. Larger 
bodies, because of greater surface, give off more heat than smaller 
ones. Men are usually larger than are women, — another reason 
why they require more food. 

The relation of digestibility to diet. Food must be digested 
in order to be used in the body. Animal foods in general can be 
more completely digested within the body than plant foods. This 
is largely due to the fact that plant cells have woody walls that 
the digestive juices cannot dissolve. Heat causes the starch 
grains to swell and thus break these woody walls. This is one 
reason for the thorough cooking of vegetable foods. Cereals 
and legumes are less digestible foods than milk and eggs. The 
agreement or disagreement of food with an individual is largely a 
personal matter. Jack Spratt, for example, cannot eat raw toma- 
toes without suffering from indigestion, while Mrs. Spratt can 
digest tomatoes but not strawberries. Each individual should 
learn early in life the foods that disagree with him and leave such 



APPETITE AND DIET 



339 



+heat 
/ 

pop corn 
xith its . 
starch, grams 



i drains ^O 

burst potato starch 
gnain5 



foods out of his diet, for " what is one man's meat may be 
another man's poison." 

The relation of appetite to diet. Every one likes some things 
better than others. Through experimentation it has been found 
that foods which are 

enjoyed cause a flow ^^>r~^ 

of digestive juices, £-7?^ 

not only in the 
mouth but also in 
the stomach. The 
sight, odor, and taste 
of food we like actu- 
ally aid in diges- 
tion. "Digestion 
waits on appetite." 
If we use common 
sense in the selec- 
tion of foods, and 
take care to avoid 

foods that We Cannot Explain what happens to starch when it is heated? When 

easily digest, we shall 
find that the appetite is often a guide in the selection of foods. 
Acidosis and how to prevent it. The body is a very delicate 
machine. Its parts must be adjusted to a nicety or trouble results. 
The blood is normally alkaline. If fat is not completely oxidized 
in the body, the partly oxidized fat remains in the tissues as a 
fatty acid. This changes the alkalinity of the blood to acidity 
and trouble immediately follows. This condition, called acidosis 
or " kotosis," is often benefited by eating fruits and vegetables 
and avoiding use of meats and fats. 



V- 



z # <z 




^g*mms enlarge 



stcrrSfe^^X y~- + oaidi break: 
changes to digestive 
Soluble sugar Jtfice 

Explain what happens to starch when it is heated? 
it is digested ? 



Self-Testing Exercise 

A man needs (1) (2) when he does hard physical 

work than when he (3) a (4) life. A (5) 

person needs more food than a (6) one, for he has more 

(7) to feed (8) plays a part in the kind as well as 

the (9) of food needed by the body. What is one man's 



340 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

meat is another man's (10), so we should learn what we can 

(11). Acidosis may be combated by a diet in which an excess 

of (12) and (13) is present. 



PROBLEM IV. WHAT IS THE BEST PROPORTION OF 
NUTRIENTS IN OUR DAILY DIET? 

The nutritive ratio. Inasmuch as all living substance contains 
nitrogen, it is evident that protein food must form a part of the 
diet; but protein alone is not a safe choice. If more protein is 
eaten than the body requires, the liver and kidneys have to 
work overtime to get rid of the excess of protein, which forms 
a poisonous waste harmful to the body. We must take foods 
that will give us, as nearly as possible, the proportion of the 
different chemical elements as they are contained in protoplasm, 
as well as an amount necessary to supply energy to the body. It 
has been found, as a result of studies by Atwater and others, 
that a man who does moderate muscular work requires nearly 
one quarter of a pound of protein, the same amount of fat, and 
a little less than one pound of carbohydrate to provide for the 
growth, waste, and repair of the body and the energy used up 
in one day. The proportion of protein in the diet is called the 
nutritive ratio. 

The protein requirement varies with the age and size of a person, 
but not with the activity. For the child, from 12 to 15 per cent 
of the total Calories should be protein. Protein is necessary for 
the building and the repair of the body. Therefore larger amounts 
are needed during growth. The child requiring 2000 Calories 
needs from 240 to 300 Calories of protein. Whereas the adult, 
who has ceased growing, needs but 10 per cent of his total in 
protein. Therefore with an energy requirement of 2500 he would 
need about 250 protein Calories. Activity has never been shown 
to break down the body cells any more than the use of the brain 
destroys brain cells. Therefore protein does not need to be in- 
creased because one is doing muscular work. Milk, meat, and 
eggs are just as essential for the school teacher as for the man who 
is doing severe muscular work. 



BASAL METABOLISM 



341 



Atwater, Chittenden, and Voit have worked out tables in 
which they have given the proportion of the various nutrients 





Calories from 
Protein 


Calories from Fat 


Calories from 
Carbohydrates 


Atwater .... 
Chittenden . . . 
Voit 


14 
10 
25 


32 
30 
20 


54 
60 
55 



that should be present in every 100 Calories of food. Any of the 
three standards might be used. 

Knowing the proportion of the different nutrients required 
as well as the foods containing vitamins and minerals, it will be 
easy for you to determine from tables (such as on pages 336-337) 
the best combinations of foods for a well-balanced diet. 

Workbook Exercises. Foods taken into the body having the pro- 
portions of the nutrients given above constitute a balanced ration 
or diet because they provide the body with the right proportion 
for tissue building as well as for fuel food. 

Compare the life you lead with that of a day laborer. Would your 
needs be the same? 

Compare your life with the life of an Eskimo in the Arctic regions. 
Would the proportion of the nutrients needed by him be the same 
as you need? Explain. 

Would the same proportion of nutrients be needed for all occupa- 
tions and in all localities? 

Are there any other factors that might cause different proportions 
of the nutrients needed by individuals? 

Would a vegetarian diet contain the protein necessary for the body? 
How would it compare with a diet containing only meat? Are there 
any reasons why a wholly vegetable diet is unwise? 

Basal metabolism. 1 The activities of a living plant or animal, 
which include all the processes that are involved in the building 
up and breaking down of protoplasm in the body, are known col- 
lectively as the metabolic processes (Gr. metabolos, changeable). 
These changes release heat as a by-product and this heat can be 
measured in calories. The heat-producing activity of the body 
during sleep or rest represents the energy which is essential for 

1 Metabolism : me-tab'6-liz'm. 



342 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

carrying on the vital processes and is known as basal metabolism. 
It is represented in a man of average weight (about 150 pounds) 
by about 65 Calories an hour. 

Method of computing energy requirement. The energy re- 
quirement of a person depends primarily upon his age, size, and 
activity. This requirement is most easily understood if expressed 
in Calories per pound per day. The following table shows the 
variation in the energy requirement of the average healthy child 
due to age. 



Ages .... 


1 


6 


10 


14 


16-18 


20 


Average Wt. . 


22 lbs. 


44 lbs. 


66 lbs. 


99 lbs. 


100-150 lb?. 


120-160 lbs. 


Calories per lb. 


45 


35 


35 


33 


20-33 


20 


Total Calories 














per day . . 


1000 


1550 


2300 


3300 


2600-4400 


2400-3200 



The above table shows that the small child needs a much larger 
amount of food in proportion to his weight than the older child 
or adult. The larger individual needs a larger amount of food 
than the smaller person, but if the weight is multiplied by the 
calories per pound, this factor is taken into account. For example, 
one fourteen-year-old boy may weigh 100 pounds and another 
140 pounds and both be healthy boys, but the larger boy will 
need a much larger amount of food. The above requirement 
will vary also with the activity of the child, the less active one 
will need less food. The difference in the energy requirement 
of an adult due to the type of activity is shown in the follow- 
ing figures : 



Type of Activity 


Average Calories per 
Pou>~d per Hour 


Sleeping or lying awake . . . 

Sitting 

Typewriting 

Standing 

Walking at moderate rate . . 
Active exercise 


one half 

two thirds 

nine tenths 

three fourths 

one and one half 

one and three fourths 






CALORIE REQUIREMENT 343 

Suppose that a man weighing 150 pounds spent his 24-hour 
day by sleeping 8 hours, sitting 8 hours, typing 2 hours, standing 
4 hours, walking 2 hours, he would require 2570 Calories a day. 

150 X i X 8 = 600 sleeping 150 X f X 4 = 450 standing 

150 X |X8 = 800 sitting 150 X 1J X 2 = 450 walking 

150 X ^ X 2 = 270 typing 

From these two tables one can easily compute his own energy 
requirement. 

Self -Testing Exercise 

The protein requirement (1) with the age and (2) 

and not with the (3). A man who does moderate muscular 

work requires nearly (4) (5) from protein, (6) 

(7) from fat, and (8) (9) from carbohydrate. 

PROBLEM V. WHAT IS THE DAILY CALORIE REQUIREMENT? 

Workbook Exercise. Check up your day's total Calories by com- 
paring it with your requirement by body weight and by the tables 
given on page 342. 

Head your paper : Name , age , weight lbs. 

Daily Calorie needs 

Amount used 

Discrepancy 

How does your day's total Calories compare with that given in the 
table of daily needs of a person of your age, doing the kind of work 
you did for the day? How can you account for any discrepancy? 

Can you suggest any improvement in your diet? Check on the 
vitamin content of your diet. 

Malnutrition. When the body cells do not receive a proper 
amount of food or the right kinds of food, then a loss in body weight 
may occur, and we say that person is undernourished, or is suffer- 
ing from malnutrition. An undernourished person is likely to be 
susceptible to disease, to tire easily, and to be sensitive to cold and 
exposure. Frequently, girls having large bones in their skeleton 
attempt to get thinner, and find all too soon that they have only 
made themselves ill without much reducing their body weight, 
which is largely due to these heavy bones. Never take up a " fad " 
diet without first consulting your own or the school physician. 



344 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

Workbook Exercise. What proportion of my daily diet goes into 
(a) basal metabolism, (6) growth, (c) activity, (d) excretion? Using 
the diagrams furnished and your own daily diet, check on your age 
and sex to see the proportion of your daily food that should go 



caloric h 


4000 
3000 
2000 
1000 












































































B^ 










































A 




















































^ 


s^. 






























£> 










years J 


23456r69 IO ll 12 13 14 15 16 17 »6 »9 20 1 



calorie 

4000 

5000 

2000 

1000 


s 










































































if 


















































A 






































































P 


£$. 






















B 


















years i 23456789 ion t£)3 14- 15 10 17 18 »9 20 





The upper chart is for boys, the lower one for girls. The relative amount of Calories needed 
for different ages are for (B), space between base line and first graph, basal metabolism 
(G) growth, (A) activity, and (E) excretion, spaces between graphs (after Holt). 

(a) into your basal metabolic needs, (b) into growth of your body, 
(c) into your daily activity (This, of course, will vary, depending on 
the kind of work you do out of school), (a) the amount that goes 
into excretion or body wastes. Remember that your growth calories 
must come from protein food and that activity should come largely 
from carbohydrates and fats. Compare carefully to see how near 
your proportions are to the ideal condition. 

Do you eat the correct proportions of nutrients to give your dietetic 
needs as shown by the charts given above ? 



CHEAPNESS OP FOODS 345 

Self-Testing Exercise 

Write the numbers of the correct answers in your workbook. 

A person asleep uses, per pound of body weight per hour, (1) one 
Calorie ; (2) f Calorie ; (3) 10 Calories ; (4) \ Calorie. 

Acidosis may be avoided by using (5) orange juice; (6) soda mint 
tablets ; (7) hot water before meals ; (8) red meats in the dietary. 

Roughage (9) helps give the body proteins ; (10) adds Calories to the 
dietary; (11) aids in regulating bowel movement. 

The protein requirement of the total Calorie requirement of the body 
is (12) 10 per cent; (13) 25 per cent; (14) 100 per cent; (15) 50 per 
cent. 



PROBLEM VI. HOW CAN THE RELATIVE CHEAPNESS OF 
FOODS BE DETERMINED? 

Practical Exercise 3. To find the relation of the value of food to its cost in 
the family dietary. Make a careful record of all purchases of food in your 
home for one week. Find out what the average weekly cost is by dividing 
the total cost by the number in your family. 

Using the tables on pages 336-337 and your daily calorie requirement, 
make out a cheap, appetizing but well-balanced menu for one person for a 
period of one week. Multiply the result by the total number in your family. 
Compare the total cost thus obtained with that worked out from your home 
dietary. 

Are you living as economically as you might ? What inexpensive substitutes 
might you introduce in place of meat? 

The relation of cost of food to diet. It is a mistaken notion that 
the best foods are always the most expensive. A study of the 
tables on pages 336 and 337 will show us that fuel and tissue- 
building materials as well as vitamins are present in foods from 
vegetable sources, as well as in those from animal sources ; and 
the vegetable foods are usually cheaper. The American people 
are far less economical in their purchase of food than most other 
nations. A comparison of the daily diets of persons in various 
occupations in this and other countries shows that as a rule 
we eat more than is necessary to supply materials for fuel and 
repair. Another waste of money by Americans is due to the false 
notion that a large proportion of the daily diet should be meat. 
Many people think that the most expensive cuts of meat are the 
most nutritious. The falsity of this idea may be seen by a careful 
study of the table on page 346. 



346 HOW DOES MAN DETERMINE THE VALUE OP FOOD? 




Table showing cost of various foods. Check these prices with present prices in your 

community. 



Preparation of foods. Much loss occurs in the improper 
cooking of foods. Meats especially, when overdone, lose much 
of their flavor and are far less digestible than when they are 
cooked properly. The chief reasons for cooking meats are that 



FOOD HABITS 347 

the muscle fibers may be loosened and softened, in which condition 
they are digested more easily, and that the bacteria and other 
parasites in the meat may be killed by the heat. The common 
method of frying makes foods difficult to digest. A good way to 
prepare meat, either for stew or soup, is to place the meat, cut in 
small pieces, in cold water, and allow it to simmer for several 
hours. Rapid boiling toughens the muscle fibers just as the white 
of egg becomes solid when heated. Boiling and roasting are 
excellent methods of cooking meat. In order to prevent the loss 
of the nutrients in roasting, it is well to baste the meat frequently ; 
thus a crust is formed on the outer surface of the meat, which 
prevents the escape of the juices from the inside. 

Vegetables are cooked in order that the cells containing starch 
grains may be broken down. This allows the starch to be reached 
more easily by the digestive fluids. Inasmuch as water may 
dissolve out nutrients from vegetable tissues, it is best to boil 
such foods rapidly in a small amount of water. This gives less 
time for the solvent action to take place. Vegetables should be 
cooked with the outer skin left on whenever it is possible. 

Practical Exercises 4. 1. Why should foods be cooked? Give three reasons. 

2. Why is a mixed diet necessary ? 

3. Name five common errors in selecting foods. 

4. Of what use are inorganic nutrients ? 

5. Of what use are condiments and flavoring substances? 

6. Of what use are soups as food? 

7. Why do we use fruit in a daily dietary? 

8. Is the use of tea or coffee justifiable in a daily diet? Why do people 
drink them ? 

9. Why are cheap cuts of meat cheap ? 

10. Defend the statement, " The average American family wastes enough 
in the kitchen to support a French family." 

Food habits. Habits play a very important part in our life 
activities. We do not think much about our daily activities, for 
once having learned the reasons for performing certain acts, those 
acts become habits. The habit of brushing teeth properly, of the 
choice of the right kinds and proportions of food, of the avoidance 
of tea and coffee, — these and other useful acts should become auto- 
matic. Some health habits that are worth acquiring are : 

(1) Have your meals at regular hours. 

(2) Take time to eat and enjoy your meals. 



348 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

(3) Chew your food thoroughly before swallowing it. 

(4) Do not take an excessive amount of any one food to the 
exclusion of others. Learn to eat a balanced diet. 

(5) Eat plenty of foods containing vitamins. 

(6) Avoid too great a proportion of highly flavored or spiced 
foods. 

(7) Avoid greasy or fried food. 

(8) Avoid foods that you know do not agree with you. 

(9) Avoid foods that you cannot digest easily and properly. 

(10) Do not eat when tired. Rest a few minutes before begin- 
ning your meal. 

(11) Drink plenty of water, at least six glasses a day, preferably 
between meals. 

Self-Testing Exercise 

Foods are cheap if they supply (1) and (2) materials 

in good quantity for the price paid (3) foods can be spoiled 

by (4) cooking. Eating the right kinds of foods in the right 

way should become a (5). 

PROBLEM VII. WHAT IS ADULTERATION? 

Pure Food Law. In 1906 Congress passed a Pure Food and 
Drugs Act that defined adulteration and remedied to some extent 
conditions in the preparation of foods that enter into interstate 
commerce. Before the passage of this act, about half of nearly 
2000 samples of food examined in several different states were 
shown to be adulterated. In Massachusetts, the State Board of 
Health made examinations of food for adulteration as early as 
1883. At that time over 60 per cent of all foods examined were 
found to be adulterated. Today both adulteration and misbrand- 
ing of food are forbidden under severe penalties. 

Demonstration 2. To study some forms of food adulteration and 
some means of detecting adulterants. 

Put some butter in a spoon and heat it over a lamp. If it is good 
butter, it will boil quietly, with much foam. Oleomargarine or poor 
butter will splutter and crackle, with little foam. 

Place half a teaspoonful of coffee to be tested on the surface of the 
cold water in the glass. Leave it for not more than five minutes. 



ADULTERANTS 349 

If the material sinks, leaving a brownish trace in the water as it sinks, 
it probably contains a large amount of chicory. If it floats for five 
minutes, it is coffee. What happens to the specimen you tested ? 

Place half a teaspoonful of mashed canned peas or beans in a beaker 
containing one teaspoonful of water and 10 drops of hydrochloric 
acid. Set the beaker in a dish of boiling water. Drop a new iron 
nail into the mixture. Boil for ten minutes. Stir constantly. If the 
nail turns green, copper has been used to color the peas. 

Put a teaspoonful of milk in a beaker. Add twice the amount of 
hydrochloric acid to which a drop of ferric chloride has been added. 
Mix by rotating the beaker gently. Place the beaker in a pan of 
boiling water and leave for five minutes. If there is a purple or 
lavender color, formaldehyde was present in the milk. 

Adulteration. The substitution of some cheaper substance, 
the subtraction of some valuable substance from a food, or 
the addition of poisonous or decomposed substances, with a 
view to cheating the purchaser, is known as adulteration. Ex- 
amples of common substitutions in foods are cottonseed oil 
for olive oil ; apple parings or core for other fruits in jellies ; sac- 
charine, which is several hundred times sweeter than sugar, 
in candy, ginger ale, and other drinks ; glucose or brown sugar 
for maple sugar; and cereals, which cost less, for meats in 
sausage. 

Other examples of added ingredients which may be harmful to 
health are arsenic, salicylate acid, borax, and boracic acid. 

Still another type of adulteration is seen in the mixing or adding 
to the substance of colors of dyes. Such artificial coloring is seen 
in the addition of copper sulphate to give a green color to canned 
vegetables, annatto to give color to butter, coal-tar dyes of many 
colors to give coloring to candy, jellies, flavoring extracts, soft 
drinks, and even meats or sausage. 

Examples of the taking away of a valuable part of the food are 
seen in the abstraction of cocoa butter from chocolate, butter fats 
from milk, or the essential oils from spices. 

Probably the food which has suffered most from adulteration 
is milk, as water can be added without the average person being 
the wiser. By means of an inexpensive instrument known as a 
lactometer, this cheat can easily be detected. Before the Pure 
Food Law was passed in 1906, milk was frequently treated with 



350 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 



substances like formalin, a harmful preservative, to keep it sweet 
for a longer time. 



FEDERAL FOOD & DRUGS ACT 



HERE ARE ITS POWERS AND LIMITATIONS REGARDING 
THE SALE OF "PATENT MEDICINES" 



IT APPLIES ONLY TO PRODUCTS THAT 
ARE MADE IN ONE STATE AND SOLD IN 
ANOTHER ( INTER STATE COMMERCE). 

IT PROHIBITS "FALSE OR MISLEADING- 
STATEMENTS ( IN OR ON THE TRADE 
PACKAGE ONLY ) REGARDING COMPOSITION 
AND SOURCE OF ORIGIN. 

IT PROH I BITS FALSE AND FRAUDULENT- 
STATEMENTS ( IN OR ON THE TRADE 
PACKAGE ONLY ) REGARDING CURATIVE 
EFFECTS. 

IT REQUIRES the manufacturers 

OF NOSTRUMS TO DECLARE ( IN OR ON THE 
TRADE PACKAGE ONLY ) THE PRESENCE AND 
AMOUNT OF ALCOHOL, MORPHINE. OPIUM, 
COCAINE, HEROIN, EUCAINE. CHLOROFORM, 
CANNABIS INDICA. CHLORAL HYDRATE AND 
ACETANILID AND THEIR DERIVATIVES. 



IT DOES NOT APPLY to products 

THAT ARE SOLD IN THE SAME STATE AS 
THAT IN WHICH THEY ARE MADE (I NTRA- 
STATE COMMERCE). 

IT DOES NOT PROHIBIT false or 

MISLEADING STATEMENTS IN NEWSPAPER 
ADVERTISEMENTS. CIRCULARS. WINDOW 
DISPLAYS, ETC. 

IT DOES NOT PROHIBIT any kind 

OF A LIE REGARDING CURATIVE EFFECTS 
IF THAT LIE IS TOLD ELSEWHERE THAN IN 
OR ON THE TRADE PACKAGE! 

IT DOES NOT REQUIRE patent 

MEDICINE" MAKERS TO DECLARE EVEN 
THE PRESENCE OF SUCH DEADLY POISONS 
AS PRUSSIC ACID, CARBOLIC ACID. ARSENIC. 
STRYCHNINE -NOR ANY OF SCORES OF 
OTHER DANGEROUS DRUGS 1 



Read this carefully. 



In what respects is this a good law ? 
in it? 



American Medical Association 
What changes would you suggest 



Self-Testing Exercise 

Adulteration is the (1) of some (2) substance in 

a food, the subtraction of some (3) substance from a food or 

the addition of some (4) substance to a food. Saccharine is a 

substitute for (5), chickory for (6), and olive oil for 

(7) (8). 



PROBLEM VIII. WHAT IS THE TRUTH ABOUT STIMULANTS 
AND NARCOTICS? 

Stimulants. We have learned that food is anything that 
supplies building material or releases energy in the body; but 
some materials used by man, presumably as food, do not come 
under this head. Such are tea and coffee. When taken in moder- 



DANGERS FROM ALCOHOL 351 

ate quantities, they produce a temporary increase in the vital 
activities of the person taking them. This stimulation is due to the 
presence of a drug called caffein which acts upon the nervous sys- 
tem as a whip acts on a tired horse. In moderation, tea and coffee 
appear to be harmless to most adults. Some people, however, can- 
not use either, even in small quantities, without ill effects. It is 
the habit of relying upon the stimulation given by tea or coffee 
that makes them a danger to man. Cocoa and chocolate, although 
both contain a stimulant, are in addition good foods, having from 12 
per cent to 21 per cent of protein, from 29 per cent to 48 per cent 
of fat, and over 30 per cent of carbohydrate in their composition. 

Demonstration 3. To show the effect of alcohol on white of egg. 

To some fresh white of egg in a test tube add, drop by drop, 50 
per cent alcohol (about the proportion in whiskey). What happens? 
Remember white of egg is like protoplasm in its chemical makeup. 
The teacher should explain that this does not happen to the body cells. 
Demonstration 4. To show the effect of alcohol on Paramecia. To 
a grooved slide containing culture of Paramecia add drop by drop some 
50 per cent alcohol. What happens at first? What happens later? 
How do you account for this? 

Is alcohol a food? The question of the use of alcohol is still 
of much interest among physiologists and doctors. Experiments 
by Professor Atwater in this country and by Durig and Millanby 
in England confirm the fact that small quantities of alcohol are 
oxidized in the body and therefore may be used in place of 
either fat or carbohydrate foods. Raymond Pearl has pointed 
out that mortality from alcohol is usually amongst the hard 
drinkers and that there is very little difference in the death rate 
between the abstainers and the moderate drinkers. But, un- 
fortunately, there are plenty of people who do not know how to 
control their appetites. 

Alcohol a poison. On the other hand, we know that although 
alcohol may technically be considered as a food, it has a harmful 
effect on the body tissues which foods do not have. According 
to Professor Chittenden, one of the great dietary experts of this 
country, alcohol, 1 although it is oxidized in the body, has a harmful 

\ Alcohol is made up of carbon, oxygen, and hydrogen. It is very easily oxidized, 
but it cannot, as is shown by the chemical formula, be of use to the body in tissue 
bxiilding, because of its lack of nitrogen. 



352 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

effect upon the liver and circulation, because it burns too fast 
and hence throws into the circulation substances which are harmful 
to health. This indicates that alcohol is a poison. Furthermore, 
statistics show conclusively that certain diseases, notably cirrhosis 
of the liver, are greatly increased by the excessive use of alcohol. 

A commonly accepted definition of a poison is : any substance 
which, when taken into the body, tends to cause the death of the 
organism or serious detriment to its health. That alcohol may do 
this is well known by scientists. No one who reads of the increase 
in the number of deaths from adulterated or " bootleg " liquor can 
draw any other conclusion than that alcohol is a dangerous sub- 
stance, especially in the form in which it is illegally sold by 
" bootleggers." " Home brews " of various kinds often have 

other poisons formed in 
them, besides alcohol, and 
thus are doubly dangerous. 

Dangers from alcohol. 
The annual table of deaths 
from alcoholism in large 
American cities, compiled by 
the Scientific Temperance 
Federation from data fur- 
nished by city health offi- 
cials, continues to show a 
smaller number of deaths 
from this cause than in the 
pre-prohibition period, 
although there has been an 
increase since the first prohibition years. The following figures 
represent the total deaths from alcoholism in nineteen cities of 
more than 300,000 population. These cities included in 1920 
about 19,000,000 of the 105,000,000 people in the United States. 



disappearance of 


year- 


% doseuXr 


isor 


7.4-1% 


1913 


647% 


1Q24- 


3.66# 


1929 


2.55% 


1 





In the last 25 years, a marked decrease in the 
number absent on Monday is noted in the records of 
a large manufacturer in the state of Delaware. 



Total Deaths from Alcoholism in Nineteen Large Cities 



1916 . . . 


. . . 1954 


1920 . . . 


... 321 


1917 . . . 


. . . 1817 


1921 . . . 


... 503 


1918 . . . 


... 820 


1922 . . . 


... 828 


1919 . . . 


... 558 


1923 . . . 


. . . 1261 



EFFECTS OF ALCOHOL 



353 



The increase in deaths after 1922 is undoubtedly due partly to 
the dangerous quality of bootleg liquor. 

The effect of alcohol on the mortality of offspring. Professor 
Laitinen, Dr. Stockard, and other experimenters have worked 
with guinea pigs and white rats to learn if alcohol has any effect 
upon the birth rate and death rate of the offspring. They found 
that the death rate is much higher in the animals born from 
alcoholic parents than in those from non-alcoholic parents. The 
rate of development of the young is faster in the non-alcoholic 
animals. In other words, the alcoholic animals were not normal. 

Susceptibility to disease increased by alcohol. A good many 
experiments have been made which prove that alcohol causes 




llxtetMtt. 126 12.3H.4 9.6 7.9 ?.1 74 15 72 7-4 7.3 7.2 32 8.6 



6 4- 




1 .. 
rtzle 



59 43 44 5.8 5.2 2.7 i& ii 18 M" ; « 5.2 3.6 29, 4.S 4a 



XeajMSU 14 IS 46 17 10 19 1920 21 



23 24 25 26 27 20 



There seems to be a close relation between the death rate per 100,000 from alcoholism 
(lower graph) and from cirrhosis of the liver, a disease caused by alcohol (upper graph). 
Since the prohibition amendment went into effect in 1019, there has been a decrease in this 
disease. 

increased susceptibility to disease. Some experiments made by 
Dr. E. G. Stillman of the Rockefeller Institute show that mice 
intoxicated with alcohol have much less resistance to pneumonia 
germs than normal mice. 

Death rates in different occupations. Reports from England, 
where certain occupations give a special temptation to drink, 
show that if 100 be accepted as an average death rate, the rate 



354 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

among brewers is 129, among hotel keepers 160, and among 
barkeepers 218. On the other hand, the death rate among clergy- 
men is only 56, for agricultural workers 60, and in the medical 
profession 88. 

Project. Try to obtain from your health department statistics which 
will enable you to get the percentage of people who die from diseases brought 
about or affected by alcohol. Estimate the number of deaths for the current 
year. Compare with the number of deaths from the same causes before pro- 
hibition. Make your comparison on a proportionate basis. 

The use of tobacco. A well-known authority defines a narcotic 
as a substance " which directly induces sleep, blunts the senses, and, 
in large amounts, produces complete insensibility." Opium, chloral, 
and cocaine are examples of narcotics. Tobacco owes its narcotic 
influence to a strong poison known as nicotine. Its use in killing 
insect parasites on plants is well known. In experiments with 
jellyfish and other simply organized animals, the author has found 
as little as one part of nicotine to one hundred thousand parts of 
sea water to be sufficient to affect profoundly an animal placed 
within it. Nicotine in a pure form is so powerful a poison that 
two or three drops would be sufficient to cause the death of a 
man by its action upon the nervous system, especially upon the 
nerves controlling the beating of the heart. It has been demon- 
strated that tobacco has, too, an important effect on muscular 
development. 

Practical Exercise 5. Why should boys in training stop smoking ? Make 
a list of the harmful results which come from smoking. 



Self-Testing Exercise 

Check the correct statements for your workbook : 

T. F. 1. Tea, coffee, and alcohol are stimulants. 

T. F. 2. Cocoa and chocolate contain no stimulating material. 

T. F. 3. Alcohol may be a food as well as a poison. 

T. F. 4. A narcotic poison induces sleep by quickening the heart 
action, thus producing insensibility. 

T. F. 5. Opium, chloral, nicotine, and cocaine are examples of nar- 
cotics. They are all habit-forming drugs. 



THE PURE FOOD AND DRUGS ACT 355 

PROBLEM IX. HOW DOES THE PURE FOOD AND DRUGS 

ACT WORK? 

Project. Make a collection of the labels of patent medicines and 
classify each under one of the heads in the following paragraphs. 
Report in class. 

Project. Make a collection of free samples of patent medicines 
and classify under the heads found in the following paragraphs. 

Drugs. A certain proportion of people are addicted to the use 
of drugs found in patent medicines. A glance at the street-car 
advertisements shows this. As is pointed out by Dr. Arthur J. 
Cramp of the American Medical Association, the United States 
patent office requires that in order to patent an article it must be 
both new and useful. This requirement would automatically pre- 
vent the patenting of practically all so-called " patent medicines " 
because they are usually combinations of drugs that have long 
been used by the medical profession and frequently given up 
by reputable physicians in favor of more effective or safer drugs. 
Patent medicines depend upon secrecy and mystery for their very 
existence. Hence they are not patented at all, for if they were 
their formulae would be open. The Pure Food and Drugs Act has 
at least caused some of the harmful products used in the formula 
to be placed on the label so that people who buy may know what 
they are getting. 

Bracers. Most of the medicines advertised contain alcohol in 
greater quantity than beer or wine, and many of them have habit- 
forming drugs in their composition. Not only are many " sarsapa- 
rillas " and " bitters " put on the market, but they are often sold 
to persons who are opposed to alcohol. A dose of one of these 
medicines usually contains about as much alcohol as the same 
amount of whisky. Such " bracers," as the American Medical 
Association have called this type of medicine, are of course habit- 
formers. Any one who begins to take them will soon become 
dependent upon them. 

Heart depressants. Another kind of medicine commonly sold 
is the poison acetanilid (as-et-an'i-lid), a powerful heart depres- 
sant contained, even at the present time, in a good many of the 
so-called headache powders. Although the Pure Food and Drugs 



356 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

Act now requires that the label show a statement of the alcohol, 
acetanilid, cocaine, opium, and certain other harmful drugs con- 
tained in a patent medicine, many people do not read the label, 
so the danger continues. What is far worse, the use of such drugs 
often leads to the drug habit. There is danger also from prussic 
acid, arsenic, and other deadly drugs not covered by the law. 

Cure-alls. Perhaps the worst thing about patent medicines is 
that they rarely cure any one, and they take an immense amount 
of money from people who can ill afford to spend it. Nearly 
$300,000,000 a year is estimated to be spent for patent medicines 
alone in this country. Many people, incurably ill with tuberculosis 
or cancer, make their condition worse through the purchase of cough 
or cancer cures, which probably contain a habit-forming drug or 
alcohol. Think how much more good the money thus spent 
would have done had it been invested in proper foods and good 
nursing, or in gaining the advice of a reliable physician. 

Due to the fact that the present law does not require the publish- 
ing of the composition of the medicine on the label, the public 
is being continually fooled into paying big prices for worthless 
or even dangerous combinations of drugs. Think of paying $3.00 
for a few cents' worth of washing soda and salt. Or $.50 for $.01 
worth of Epsom salt. Yet this is being done every day. To 
paraphrase a great showman : " There are some people who 
always want to be fooled." Are any friends of yours in this 
class ? 

One of the reasons why people buy patent medicines is because 
they read the glowing testimonials written by people who say 
they have been cured by patent medicines. Investigation of 
such letters often shows that they have been written by people 
who were paid for writing them. There is a regular business in 
the buying and selling of patent medicine testimonials. Such 
testimony is worthless, and in cases where the testimonial is written 
in good faith how do we know that the person who wrote it really 
did receive the benefits testified to from that particular medicine. 
Frequently we know he did not because death notices of people 
who wrote, saying that they have been cured of tuberculosis or 
kidney trouble by this or that nostrum, have been found in the 






TESTS 357 

same issue of the paper containing the testimonial which says " I 
have been cured." The moral is : do not believe the testimonial. 

Self-Testing Exercise 

Check the correct statements for your workbook : 

T. F. 1. The Pure Food and Drugs Act requires that the trade 
package declare the presence of all poisonous drugs in a patent medi- 
cine. 

T. F. 2. The Pure Food and Drugs Act prohibits fake or mislead- 
ing statements in newspapers and circulars concerning the curative 
powers of a drug. 

T. F. 3. Testimonials are valuable because they prove that persons 
are cured of disease by patent medicines. 

T. F. 4. " Bracers " are valuable because they help people to forget 
their troubles. 

T. F. 5. Some people may be cured by patent medicines. 

Review Summary 

Check your knowledge of this unit by : (1) rechecking the survey questions ; 
(2) performing all assigned exercises ; (3) checking with your teacher the scores 
of the various tests and doing over the parts you missed ; and finally (4) making 
an outline for your notebook. 

Test on Fundamental Concepts 

In vertical column under the heading CORRECT write numbers of all statements you be- 
lieve are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 2§. 

I. Foods (1) may contain organic nutrients, salts, vitamins, and 
water ; (2) are never oxidized in the body ; (3) always build tissues ; 
(4) should never be used unless they contain vitamins ; (5) are neces- 
sary for growth, work, and well being. 

II. Proteins (6) are necessary for growth; (7) must contain the 
amino acids necessary for tissue building if they are to be called com- 
plete; (8) may contain several or all eighteen amino acids; (9) in 
gelatin furnish tissue-building material; (10) in milk contain all the 
amino acids necessary for growth. 

III. Foods (11) containing vitamin A promote growth and prevent 
the eye disease called xerophthalmia; (12) when taken in the right pro- 
portions, form a balanced ration ; (13) containing vitamin B prevent 
loss of sleep; (14) containing vitamin C prevent scurvy; (15) will 
never contain vitamin D unless they are placed in the sunlight. 



358 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 

IV. The factors which determine the amount of food one should 

eat are (16) the kind of work he does; (17) the size of his skeleton; 
(18) his age; (19) where he lives and the time of year; (20) his 
appetite. 

V. A diet is well balanced (21) when it contains all the vitamins; 
(22) when 10 to 20 per cent of its Calories are protein; (23) when it 
has the right proportion of nutrients to make living matter and supply 
the body with energy for the kind of work we have to do ; (24) when 
the food is properly cooked ; (25) when it contains all the nutrients. 

VI. The Pure Food and Drugs Act (26) prevents the use of patent 
medicines ; (27) prevents the use of stimulants ; (28) prohibits false 
or fraudulent statements (on trade packages only) regarding the 
curative effects of patent medicines; (29) has prevented the use of 
certain harmful drugs ; (30) applies only to the products which are made 
in one state and sold in another. 

VII. Alcohol (31) is a narcotic poison; (32) is a food, because it 
can be oxidized in the body ; (33) is found in many patent medicines ; 
(34) causes greater susceptibility to disease ; (35) never hurt anybody. 

VIII. Patent medicines (36) are safe to take if you know what they 
contain; (37) rarely cure and may do much harm; (38) must state 
on the label the presence of such deadly drugs as arsenic, strychnine, 
and prussic acid ; (39) must state on the label the presence of alcohol, 
morphine, opium, and cocaine ; (40) often have false claims made for 
them in the newspapers and such statements are lawful. 

Achievement Test 

1. What is the difference between a nutrient and a food? 

2. Why are some proteins better tissue-building foods than others ? 

3. How can you make a dietary containing the necessary vita- 
mins? 

4. What are " the essentials of an adequate food supply "? 

5. What foods are harmful to you? 

6. How do you judge a cheap and an expensive food? 

7. What are your own calorie needs? 

8. How would you make up an individual 100-Calorie dietary giv- 
ing the correct proportions of carbohydrates, fat, and proteins ? 

9. What are the strong and weak points of the present Pure Food 
and Drugs Act? 

10. What is an adulterant under the law? 



TESTS 359 

11. How would you make five tests for the detection of adulterants ? 

12. What are both sides of the alcohol question? 

13. What proof have we that alcohol is a poison? 

14. What are the chief types of fakes in the patent medicine game ? 



Practical Problems 

1. Give examples of ten cheap foods that are good foods. Justify 
your statement. 

2. It is said that an American eats twice as much meat as a French- 
man. Are there any reasons why he should do this ? 

3. A boy weighing 125 lbs. uses about 150 Calories in slowly walking 
3 miles. How many Calories will he use in taking a 10-mile hike? 
Suppose he should speed up his rate of walking. Would he use more 
Calories for the same distance? 

4. Estimate your own Calorie needs for a hike of 12 miles, walking 
moderately all the way. 

5. If food costs 5 cents per 100 Calories, would it be cheaper to pay 
8 cents for carfare or walk a mile and a half to school ? 

6. Suppose you were ill and had to use milk as a food. How much 
milk per day would you have to take to supply your basal metabolism 
for 24 hours? 

7. Make a collection of patent medicine labels to show the various 
kinds and amounts of alcohol and poisons contained therein. Classify 
them according to the harm they do; according to the drugs they 
contain. 



Useful References 

Ellis and Macleod, Vital Factors of Foods, Vitamins and Nutrition. 
(D. Van Nostrand Co. 1915.) 

Farmers' Bulletins, 23, 34, 42, 85, 93, 121, 128, 132, 142, 182, 249, 
256, 295, 298, 717, 817, 824, 975, 1313, 1383. 

Funk, The Vitamines. (Williams & Wilkins. 1922.) 

Harrow, Vitamines. (E. P. Dutton & Co. 1922.) 

Hunter, Laboratory Problems in Civic Biology. (American Book Com- 
pany.) _ 

Lusk, Science of Nutrition. (W. B. Saunders Co.) 

Nostrums and Quackery. American Medical Association, Chicago. 

O'Shea, Tobacco and Mental Efficiency. (The Macmillan Co. 1923.) 

Sherman, Chemistry of Food and Nutrition. (The Macmillan Co. 1926.) 

Starling, Hutchinson, Mott, Pearl, The Action of Alcohol on Man. 
(Longmans Green & Co. 1923.) 

Stiles, Nutritional Physiology. (W. B. Saunders Co. 1924.) 




SURVEY QUESTIONS 

Why do you chew food ? What do we mean by the term " digestion " ? 
Do you know what does the digesting of food? Do plants digest their 
foods ? Where do we digest foods ? How and why do we digest foods ? 
Do you know how to avoid having indigestion ? 



Photo by H. Armstrong Roberts 



UNIT XII 



HOW FOOD IS PREPARED FOR BODY USE 



Preview. It seems a far cry from the chemistry laboratory, 
with its bottles and test tubes, its acids and its bases and all of 
the complicated formulae that we see in chemistry books, to our 
own digestive tract. But to the physiologist the human body 
is a marvelous chemical laboratory which in the complexity 
of its working makes our science laboratory in school seem very 
insignificant. We have learned that organic food substances are 
found in the leaves of plants. This food has to be taken to other 
parts of the plant in order to be used. Before it can be trans- 
ported from one part of the plant to another, it has to be made 
soluble so that it can pass from one cell to another by the process 
of diffusion through a cell membrane. This change of food from 

360 



WHAT IS A GLAND? 361 

an insoluble to a soluble form, you remember, was brought about 
by agents called enzymes. Several different kinds of enzymes were 
found in the plant cells, and in those cells digestion took place. 

Somewhat the same condition exists in animals. If food is to 
be of use to man, it must be changed into a soluble form that 
can pass through the walls of the alimentary canal, or food tube. 
This process is carried out by the various enzymes which bring 
about digestion. 

In nearly all vertebrate animals, food is taken into the mouth and 
passed through a food tube, in which it is digested. This tube is 
composed of different portions, named, respectively, as we pass 
from the mouth downward, pharynx (far 'inks), gullet, stomach, 
small intestine, and large intestine. Attached to this food tube 
or lying in its walls are structures called glands. It is within the 
cells of these glands that the enzymes are manufactured which 
cause digestion to take place. 

PROBLEM I. WHAT IS A GLAND AND HOW DOES IT DO 

ITS WORK? 

In addition to the alimentary canal proper, and connected with 
it, we find a number of digestive glands. These are the salivary 
glands of the mouth, the gastric glands of the stomach, the pan- 
creas (pan'kre-as) and the liver, both connected with the small 
intestine by ducts, and the intestinal glands in the walls of the 
small intestine. Besides these glands which aid directly in diges- 
tion, there are several others known as the endocrine (en'd6-krln) 
or ductless glands, because they have no ducts or tubes to carry off 
their contents. These glands give their secretions, which contain 
substances known as hormones, directly into the blood. We shall 
study their functions later. 

Demonstration It A simple gland. (Microscopic preparation.) 
Under the microscope, notice the structure of a gland in both cross 
and longitudinal sections. With what is the wall lined? What is 
the shape of the gland ? If work is done by a gland, then it must have 
fo,od to do this work. Might the material poured out of a gland be 
manufactured from the food it gets ? 

What structures would of necessixy go to a gland to take food there? 
Write a paragraph telling the uses and structure of a gland. 



362 



HOW FOOD IS PREPARED FOR BODY USE 



"blood 



i~ _; /C.-Cotpillary 



Structure of glands. In its simplest form a gland may be a 
collection of cells which, by means of their own activity, manu- 
facture and pour out a substance known as a secretion. The 
nectar gland of a flower is such a collection of cells. In animals, 
glands are usually tubular, such as the gastric gland shown on 
page 371, or like little sacs, as in the diagram. In all animal 
glands there is a rich blood supply to and from the secreting cells 

it , that line the tubes or sacs, and 

mouth of . 

planet tiny nerves which control the 

gland cells and blood supply. 

Enzymes and their work. 
Certain gland cells form secre- 
tions containing the chemical 
activators called enzymes, which 
we have already learned cause 
digestion in plants. In animals 
the enzymes secreted by the 
cells of the glands and poured 
out into the food tube act upon 
insoluble foods so as to change 
them to a soluble form. They 
are the product of the activity 
of the cell, although they are 
gIand not themselves alive. We do 
not know much about enzymes 
themselves, but we can observe what they do. Some enzymes 
render certain foods soluble, others work in the blood, and 
still others probably act within the cells of the body as an aid 
to oxidation, when work is done. Enzymes are very sensitive 
to changes in temperature and to the degree of acidity or 
alkalinity of the material in which they act. We shall find that 
the enzymes from glands in the walls of the mouth will not be 
active very long in the stomach after the change from the alkaline 
medium in the mouth to the acid medium in the stomach. En- 
zymes seem to be able to work indefinitely, provided the surround- 
ings are favorable. A small amount of digestive enzyme, if it 
had long enough to work, could digest a large amount of food. 




lvraph spaa 



A gland cut lengthwise. Explain how 
might obtain its secretions. 



SALIVARY GLANDS 363 

Demonstration 2. To show the use of digestion. 

In one thistle tube place some saliva mixed with starch paste. In 
a second tube place some paste and water. Fasten membrane covers 
over the thistle tubes, and wash carefully all starch or other material 
on outside of tube. Then place the two thistle tubes, large end down, 
in a beaker containing just enough warm water to cover the membrane 
on the tubes. 

Next test some saliva with Fehling's solution. Is there any grape 
sugar present? 

At the end of the laboratory period test the contents of the beaker 
with iodine and with Fehling's solution. Was there any starch in the 
water ? Was there any grape sugar ? How did it get into the beaker ? 

Salivary glands. We are all familiar with the substance called 
saliva which acts as a lubricant in the mouth. Saliva is manu- 
factured in the cells of three pairs of glands which empty into the 
mouth, and which are called, according to their position, the 
parotid (beside the ear), the submaxillary (under the jawbone), 
and the sublingual (under the tongue). 

Self-Testing Exercise 

The glands necessary for digestion are the . . (1) (2), 

(3), (4), and (5). They secrete (6) 

that cause digestion of the (7). Starches are changed to 

(8) by enzymes in the (9) . Glands may be in the 

form of (10) or (11). Small (12) control 

the (13) cells and the blood (14) to them. 



PROBLEM II. WHAT IS THE STRUCTURE AND WORK OF 
THE MOUTH CAVITY? 

Laboratory Exercise. Comparison of mouth of a frog and of a 
man. Compare the. open mouth of the frog with the diagram. Do 
the same studying of your own mouth. Can you find all structures 
shown in the diagrams? 

In man the mouth cavity and the internal surface of the food 
tube are lined with mucous membrane. The mucus secreted from 
gland cells in this lining makes a smooth surface so that the food 
can slip down easily. The roof of the mouth is formed by a plate 
of bone called the hard palate, in front, and a softer continuation 



364 



HOW FOOD IS PREPARED FOR BODY USE 



to the back, called the soft palate. These separate the nose 
cavity from that of the mouth. The space back of the soft 
palate is called the pharynx, or throat cavity. From the pharynx 





.hard palate 
soft palate 

.- uvulae 



..-nccr-ee 

...vomer 



.--Eustachian - 

"tube 
—esophagus--! 
'—glottis 
— tongue - 



Comparison between the mouth of frog and of man. 

lead off the gullet and trachea or windpipe. There are also open- 
ings here to the Eustachian tubes and to the nose. The lower 
part of the mouth cavity is occupied by a muscular tongue. The 
tongue is used in moving food about in the mouth, and in starting 

it on its way to the 
gullet. 



Laboratory Exercise. 
What conditions are 
favorable or unfavor- 
able for the digestion 
of starch? Place in 
test tubes an equal 

. i . m amount of starch paste, 
epiglottis- In the firgt tube add 

water ; to a second, 
saliva; to a third, 
saliva and a few drops 
of weak acid ; to a 
fourth tube saliva and 
a base such as weak 
sodium hydroxide. 
Place all these tubes 
in water of about 
99° F. for 20 minutes. 
Test the contents of 



hard 
soft 




A longitudinal section through the head, showing the 
throat and its connections. How is the throat connected 
with the nose ? with the stomach? with the lungs ? 



THE TEETH 



365 



each tube with Fehling's solution. In which tube or tubes has 
digestion taken place? 

Take two test tubes, place in each tube an equal amount of starch 
paste and saliva. Place one tube in warm water, the other in the ice- 
box. Test each for grape sugar after one hour. In which tube do you 
find sugar? The above experiments show that the enzymes in the 
saliva under certain conditions change starches to sugars. You will 
remember that starch in the growing corn grain was changed to grape 
sugar by an enzyme called 
diastase. In saliva a similar 
action is caused by an 
enzyme called ptyalin (tl'a- 
lin), or salivary amylase; but 
this enzyme acts only in an 
alkaline medium at about 
the temperature of the body. 

The teeth. The teeth of 
man, unlike those of the 
frog, are used in the me- 
chanical preparation of the 
food for digestion. Instead 
of holding prey, they crush, 
grind, or tear food so that 
more of its surface may be 
exposed to the action of 
the digestive fluids. The 
first or " milk " teeth of 
man are only twenty in 
number, while the second 
or " permanent " set contain thirty-two teeth. These teeth are 
divided, according to their structure, into four groups ; these are 
the incisors, or cutting teeth; the canines; the premolars; and 
the flat-top molars, or grinding teeth. 

Each tooth, as the figure shows, is composed chiefly of hard 
bone or dentine. The crown of the tooth is covered with enamel, 
the hardest substance in the body. In the interior is a pulp 
cavity, which during the life of the tooth contains nerves and blood 
vessels which give the tooth its nourishment. The tooth is held 
in its bony socket in the jaw by cement. 

When a tooth dies, bacteria often set up an irritation at its base 




Draw this diagram in your workbook and indi- 
cate the four kinds of teeth in their place in the 
jaw. 



366 



HOW FOOD IS PREPARED FOR BODY USE 



and form a center or focus of infection from which poison gets 
into the blood. As a result of this, very serious diseases may 

occur, of which the most com- 







exiamzA 

dentine 

pulp 



mon are rheumatism of the 
joints and neuritis or inflam- 
mation of the nerves. Infected 
teeth should be extracted, as 
this usually removes the cause 
of the trouble. 



."blood, , 
vessel 

.cement* 



Practical Exercise 1. Using a 
small mirror, count your teeth, 
giving the number under each of 
the following heads : 

(a) Incisors, broad cutting teeth 
in front. 

(&) Canines, pointed sharp teeth 
next to the incisors. 

(c) Premolars, grinders with two 
points on the biting surface. 

(d) Molars, teeth with more than 
two points, in the back of the 
mouth. 

Practical Exercise 2. Examine 

carefully with a flash light each of 

A section through a tooth. Why is a cavity your teeth and answer the following 

painful? Why is a tooth sometimes so hard questions. Mark the points asked 

t0 pul1 ? for on the chart copied from the 

diagram. 
With a bracket, label each group of teeth. With a cross, mark all the 
teeth you have lost or that have not grown. Mark all cavities not filled in 
your teeth by a spot where the cavity exists. If teeth have been filled, 
mark with appropriate title. 

Care of the teeth. Too much emphasis cannot be placed on 
the proper care of the teeth. They should be carefully brushed 
each morning and evening. Use a medium stiff brush and work 
the bristles in a vertical direction away from the gum so as to get 
between the teeth. After that, a rotating movement over the sur- 
face and between the teeth will dislodge any remaining particles 
of food. Above all, massage the gums with your brush and polish 
the surface of the teeth both in back and in front, for this helps 
remove the bacterial film. Dental silk should be used after meals. 

It has been found that fruit acids are very beneficial to the teeth. 
Vinegar diluted to about half strength with water makes an 



PARTS OF THE DIGESTIVE TRACT 367 

excellent dental wash. If one has an acid mouth, a good tooth 
paste mixed with castile soap may be used to clean the teeth. 

The teeth should be cleaned by a reliable dentist at least every 
six months. In this way deposits which cover the teeth may be 
removed and decay prevented. If decay once starts, sooner or 
later the tooth will be lost. 

Practical Exercises 3. What are the uses of (a) the incisors, (6) the canines, 
(c) the premolars, and (d) the molars ? 

How many teeth are there in the first set of teeth? When do they begin to 
come, and when do they go ? 

What makes teeth decay ? Why should we clean the teeth night and morn- 
ing ? How should we brush them ? 

What is a focal infection ? What harm may it do ? What harm might 
come from swallowing fluids which pass through a mouth containing decayed 
teeth? 

How often should one visit the dentist ? Why ? 

Self-Testing Exercise 

Food passes from the (1) into the (2) and (3) 

on its way to the stomach. The enzymes in (4) change 

(5) to sugars. A tooth is composed chiefly of (6). 

The crown of the tooth is covered with (7). The interior of 

the tooth is called the (8) (9). A decayed tooth 

may be the source of a (10) (11). The saliva 

contains the enzyme, (12). 

PROBLEM m. WHAT ARE THE PARTS OF THE DIGESTIVE 

TRACT? 

If we are to understand the work of the parts of the food tube, 
it is necessary that we know something about their structure. 
One can learn about the digestive tract through the study of charts 
or models, but it is much easier to understand if we can see its 
parts as they would really appear in a living person. This we 
cannot do, but we have a good substitute in the frog. Let us 
examine the digestive tract of a frog in order to compare it with 
man. 

Laboratory Exercise. To compare the digestive system of a frog 
with that of man. 

Opened frogs preserved in 4 per cent formalin. Manikin showing- 
digestive tract. 



368 



HOW FOOD IS PREPARED FOR BODY USE 



Note in the frog the glistening membrane (peritoneum) lining the 
body cavity. A similar membrane is found in man. 

In man, the body cavity or space in which the internal organs rest 
is divided into two parts by a wall of muscle, the diaphragm, which 
separates the heart and lungs from the other internal organs. In the 
frog no muscular diaphragm exists. Numerous blood vessels can be 
found in the frog, especially in the walls of the food tube, which carry 
the digested nutrients to other parts of the body. 

Notice the large, reddish brown organ covering most of the other 
organs. This is the liver. Count the lobes or divisions of the liver 
and compare the position and general structure with the liver of man 
(use manikin). Lift up the middle lobe of the liver and find the gall 
bladder, a greenish sac. This contains bile, a secretion from the liver. 
Now compare with the manikin to see if you can locate where the bile 
gets into the food tube. 

The food tube begins at the mouth, continues as a short, wide gullet 
into the stomach (just under the liver). Compare these structures in 
the frog with similar structures in man. The stomach of the frog 
leads into a long coiled small intestine and thence into a very short 
large intestine. The large intestine not only excretes the solid wastes of 
the body, but it is also the reservoir for nitrogenous wastes. It thus differs 
from a true large intestine and is called a cloaca. 




....gullet 
----liver-- 

A..gall blacCder. 
-j--ston?ack-. 



pancreas. 



smctll 
intestine 




■ L*\ :^\£mtSn:\ ;4 ■■■: I 



appendix 



aau^. 




Compare part by part, the digestive tract of the frog with that of man. Are there any structures 
found in one and not in the other? 



THE DIGESTIVE TRACT OF MAN 369 

Note that all the organs are held in place by a fold of the body- 
cavity lining called the mesentery. What is its use ? A cream-colored 
body, the pancreas, can be located between the stomach and the first 
bend in the small intestine. 

The digestive tract of man. Comparing the food tube of man 
and its glands part by part with that of the frog, we find a striking 
similarity as to parts. The lower part of the digestive tube in the 
frog is relatively much shorter than that of man, whose small in- 
testine is about 20 feet in length. The large intestine is also rel- 
atively shorter. We find that in general the uses of the parts are 
quite similar in spite of their difference in size and the method of life. 

Self-Testing Exercise 

The digestive tract of man consists of a (1), beginning 

at the (2) and ending at the (3). Ducts from several 

(4) which aid in digestion empty into it. The parts of the 

food tube are (5), (6), (7), (8), 

(9) and (10) (11). The largest glands 

are the (12) and (13). 



PROBLEM IV. WHAT DIGESTIVE CHANGES TAKE PLACE IN 
THE STOMACH? 

Demonstration 3. To determine the conditions most favorable for 
gastric digestion. 

Use five test tubes or beakers and some boiled white of egg. In the 
first tube put minced white of egg and water ; in the second minced 
white of egg and 0.2 per cent hydrochloric acid ; in the third, fourth, 
and fifth minced white of egg, 0.2 per cent hydrochloric acid, and 
pepsin. 

Keep the first three in a warm place at about a temperature of 
blood heat for several hours. Keep the fourth in an ice box or sur- 
rounded by cracked ice. Keep the fifth in boiling water for 15 or 20 
minutes, then place it in the warm place with the first, second, and 
third. 

Test the first with biuret test 1 for the presence of a soluble protein 
(a peptone). Test the second, third, fourth, and fifth with biuret 
test and note results. 

1 Biuret solution : To the material to be tested add its own bulk of concentrated 
caustic soda. Then add a drop or two of weak copper sulphate solution. A 
violet or blue color shows the presence of unchanged protein, a rose pink the 
presence of peptone. 



370 



HOW FOOD IS PREPARED FOR BODY USE 



What conditions are necessary for the digestion of protein ? What 
is the effect of an extreme heat and cold on the action of hydrochloric 
acid and pepsin with a protein? Make a table giving all results of 
the above tests of conditions necessary for the digestion of protein. 

Chewing and swallowing. After food has been chewed and 
mixed with saliva, it is rolled into little balls and pushed by the 
tongue into such position that the muscles of the throat cavity 
may seize it and force it downward. Food, in order to reach the 
gullet from the mouth cavity, must pass over the glottis which is 
the opening into the trachea. When food is in the process of 
being swallowed, the upper part of the gullet forms a trapdoor 
over this opening. When this trapdoor, called the epiglottis, is not 
closed, and food " goes down the wrong way," we choke, and the 
food is expelled by coughing. 

The esophagus. After food leaves the mouth cavity, it gets 
beyond our direct control, and the muscles of the gullet, stimulated 
to activity by the presence of food in the tube, push the food down 

by a series of slow-moving 
muscular contractions until it 
reaches the stomach. These 
wavelike movements, peri- 
stalsis, occur also in the stomach 
and the small intestine. Peri- 
staltic movement is caused by 
2) muscles which are not under 
voluntary nervous control, al- 
though anger, fear, disgust, 
or other unpleasant emotions 
may slow them or even stop 
them entirely. 

Stomach of man. The 






E 



_^5""^^™__ 



££ 



-g — J > Js*i*&£-2-2-g- 



Food passes through the digestive tract by stomach is a pear-shaped organ 

means of a series of successive wavelike move- , , » , , ,. , , ., 

ments, which are under the control of the Capable 01 holding aDOUt three 

nervous system. The constricted portion is _:_i Q Onnrnsitp in tViP oiillpt 

always preceded by an area of relaxation. P lntS ' opposite t O tne gUliet, 

the end which empties into 
the small intestine is provided with a ring of muscle called the 
pylorus (pi-lo'r#s). When this muscle relaxes, it permits the 



GASTRIC GLANDS 



371 



neck of the glonct 

.HCl-Secretiiag 
cell on inner* 
imcrrgin of gland 



t*a>v 

■materials 

am, 



passage of food from the stomach. There is also another ring 
of muscle guarding the entrance to the stomach. 

Gastric glands. The folded wall of the stomach is dotted with 
thousands of tiny pits, the mouths of the gastric glands. The 
gastric glands are little . 1 

tubes, the lining of m SL §J tfLnSSfa* 

which secretes the 
gastric juice. When 
we see or even think of 
appetizing food, this 
secretion is given out 
in considerable quan- 
tity. Just as the 
mouth " waters " at 
the sight or thought 
of certain well-liked ^fj 5 * 
foods, the gastric by the 
glands of the stomach 5 t r<2 ; 
also pour out their 
secretions under simi- 
lar stimuli. Gastric 
juice is slightly acid 
in its chemical reac- 
tion, containing about j 
0.2 per cent free 
hydrochloric acid. It 
also contains two 
enzymes : one very 
important, called 
pepsin, and the other, less important, called rennin. Rennin 
curdles or coagulates a protein found in milk; after the milk is 
curdled, the pepsin is able to act upon it. " Junket " tablets, 
which contain rennin, are used sometimes in the preparation of a 
dessert from milk. 

Action of gastric juice. If proteins are treated with artificial 
gastric juice at the temperature of the body, they will become 
swollen and then gradually change to substances (peptones) which 




..cell secreting* 
f luridC Containing 



C-hody of the gland 

*vhere most of the 

secreting is done 

Gastric glands secrete a substance which is changed into 
pepsin in the presence of acid. The secretion of these glands 
forms the gastric fluid. 



372 HOW FOOD IS PREPARED FOR BODY USE 

are soluble in water. This is due to the action of the enzyme 
pepsin. 

The hydrochloric acid found in the gastric juice acts upon lime 
and some other salts taken into the stomach with food, changing 
them so that they may pass into the blood and eventually form 
the mineral part of bone or other tissue. This acid also has a 
decided antiseptic influence in preventing growth of bacteria, some 
of which cause decay, others of which cause disease. 

Experiments on digestion in the stomach. Some very interest- 
ing experiments have been made by Professor Cannon of Harvard 
with reference to the movements of the stomach contents. Cats 
were fed with a material having in it subnitrate of bismuth, a 
harmless chemical that is visible under the fluoroscope. It was 
found that shortly after food reached the stomach, a series of 
waves began which sent the food toward the pyloric end of the 
stomach. If the cat was feeling happy and well, these contrac- 
tions continued regularly, but if the cat was cross or bad tempered, 
the movements would stop. These experiments were repeated on 
men, with like results, and show the importance of cheerfulness 
at meals. Pleasant conversation and a cheerful mind at the table 
will go far toward making the food taste better and also toward 
causing it to digest properly. 

Other experiments showed that food which was churned into 
a soft mass was permitted to leave the stomach only when it 
became thoroughly permeated by the gastric juice. It is the 
acid in the partly digested food that causes the pyloric ring of 
muscle to open and allow the food to escape little by little into the 
small intestine. 

Self-Testing Exercise 

The food passes through the (1) and (2) by a series 

of (3) (4). The stomach is a (5) organ. 

The (6) (7) secrete a (8) which empties 

into the (9). This (10) is slightly (11) in 

chemical reaction, and contains two enzymes, (12) and 

(13). The enzyme (14) digests the (15) 

in the stomach. Our digestion is affected by our (16). 



THE PANCREAS 373 

PROBLEM V. WHAT WORK IS DONE BY THE PANCREAS? 

Demonstration 4. What is the action of pancreatic juice on starch? 

Add some artificial pancreatic juice (made by mixing 5 grains of 
pancreatin and 10 grains of baking soda in 100 c.c. of water) to some 
dilute starch paste. Keep it at about body temperature for a few 
hours, then test with Fehling's solution. What occurred when Feh- 
ling's solution was added? What was the action of pancreatic juice 
on starch? 

Demonstration 5. What is the effect of pancreatic juice on protein ? 

Using artificial pancreatic juice instead of a mixture of hydrochloric 
acid and pepsin, carry out an experiment as described for the test for 
the third tube in the Demonstration on page 369. Was any of the 
white of egg digested? 

Demonstration 6. What is the effect of pancreatic juice on oils and 
fats? 

Shake up oil and water. What happens? Then add a little alka- 
line substance, e.g., baking soda. What happens? Xow shake up 
water with artificial pancreatic juice. What happens? What is the 
effect of pancreatic fluid on oils? 

Make a table to show the effect of pancreatic juice on nutrients. 

Position and structure of the pancreas. The partly digested 
food in the small intestine comes in contact almost simultaneously 
with secretions from the liver, the pancreas, and the intestinal 
glands. We shall first consider the function of the pancreas. 
The pancreas is one of the most important digestive glands in the 
human body. It is a rather diffuse structure, resembling the 
salivary glands. Its duct (joined with the bile duct from the 
liver) empties into the small intestine a short distance below 
the pylorus. 

Work done by the pancreas. Starch paste added to artificial 
pancreatic fluid and kept at blood heat is soon changed to sugar. 
Proteins, under the same conditions, are broken down into the 
amino acids. Fats, which so far have been unchanged except to 
be melted by the heat of the body, are changed by the action of 
the pancreatic fluid and the bile into substances which can pass 
through the walls of the food tube. If we test pancreatic fluid, 
we find it strongly alkaline in its reaction. If two test tubes, one 
containing olive oil and water, the other olive oil and a weak 
solution of caustic soda (w T hich has an alkaline reaction), are 
shaken violently and then allowed to stand, the oil and water will 
quickly separate, while the oil and solution of caustic soda will 



374 



HOW FOOD IS PREPARED FOR BODY USE 



remain for some time in a milky emulsion. If this emulsion is 
examined under the microscope, it will be found to be made of 

millions of little droplets of 
fat, floating in the liquid. 
The presence of the caustic 
soda helped the forming of 
the emulsion. Pancreatic fluid 
emulsifies fats and changes 
them into fatty acids and 
soft soaps. Fat in these forms 
can be absorbed. The above 
changes are brought about 
by three enzymes : amylase 
(am'i-las), which breaks down 
starches to simpler sugars ; 
trypsin (trip'sm), which, 
working with other enzymes 
of the small intestine, breaks 
protein into amino acids ; 
and lipase (lip'as), which 
breaks the fats into fatty acids and glycerin. These fatty 
acids become soap when mixed with the alkaline material in 
the intestinal juice. 

Conditions in which the pancreas does its work. The secre- 
tion of the pancreatic juice is brought about by the action of a 
hormone called secretin. This substance, which is formed in some 
of the cells lining the small intestine just below the pylorus, is 
released into the blood at the time food passes from the stomach 
through the pylorus. This food is acid, and the acid, on touching 
the lining of the small intestine, causes the formation of secretin 
in its walls. This secretin passes into the blood and stimulates 
the pancreas and liver to release their fluids. This is an example 
of hormone control. 




Milk, a form of emulsion, as seen under the 
microscope. The fat globules appear in groups. 
The circle shows one group of globules highly 
magnified. 



Self-Testing Exercise 



The pancreatic fluid changes (1) to 

(3) to (4) (5), and 



(6) 



...(2); 
into . . 



(7) 



FUNCTIONS OF THE LIVER 375 

(8). These changes are caused by the enzymes, (9), 

(10), and (11). The hormone (12) causes 

the pancreas to secrete (13) (14), which is 

(15) in its reaction. 






PROBLEM VI. WHAT ARE THE FUNCTIONS OF THE LIVER? 

Liver. The liver is the largest gland in the body. In man, it 
is found just below the diaphragm, a little to the right side of the 
body. The liver is not primarily a digestive gland, although it 
secretes daily about a quart of bile. Bile contains no enzymes, 
although it may have the power of rendering more active the 
enzyme in the pancreatic fluid that acts upon fats. Certain sub- 
stances in the bile aid especially in the absorption of fats. Bile 
seems to be mostly a waste product from the blood. The color 
of bile is due to certain waste substances which come from the 
destruction of worn-out red corpuscles of the blood. This destruc- 
tion takes place in the liver (and also in the spleen, sl large ductless 
glandlike organ near the stomach). The bile stimulates the 
peristaltic movements of the intestine, thus preventing extreme 
constipation. It also has a slight antiseptic effect in the intestine. 

The liver a storehouse. 
Perhaps the most important 
function of the liver is the 
formation and storing of a 
material called glycogen, or 
animal starch. The liver is 
supplied with blood from two 
sources. Some comes from 
the heart, but a greater 
amount comes directly from 
the walls of the stomach and 
intestine (see diagram on 
page 378) . The liver normally 
contains about one fifth of all 
the blood in the body. This blood is very rich in food ma- 
terials, and from it the cells of the liver take out sugars to form 




pancreatic 



What glandular secretions aid in the digestion of 
the food in the small intestine ? 



376 HOW FOOD IS PREPARED FOR BODY USE 

glycogen. 1 Glycogen is stored in the liver until such a time as a 
food is needed that can be quickly oxidized ; then it is changed 
to sugar and carried off by the blood to the tissue which requires 
it, and there used for this purpose. Glycogen is also stored in 
the muscles, where • it is oxidized to release energy when the 
muscles are exercised. 

Self-Testing Exercise 

The liver stores (1), which is later changed into (2) 

when the tissues need it. The bile is secreted by the (3). 

It is a (4) (5) from the blood and it probably 

(6) in the absorption of (7) . The liver contains 

about (8) (9) of all the blood in the body. The 

bile (10) the -(H) movements of the intestine. 

PROBLEM vH. HOW ARE FOODS ABSORBED AND HOW DO 
THEY GET INTO THE BLOOD? 

Laboratory Exercise. How is the surface of the digestive tube 
increased ? 

Study the structure of tripe (stomach wall of a ruminant) and the 
microscopic slide of a cross section of the small intestine. Remember 
that the chief function of the small intestine is to get food into the 
blood. 

Make a tube of paper having a diameter of one inch. Then try to 
make a tube having the same diameter but having a fluted wall. 
Which takes more paper? Which would present more surface? 
Study the diagram of a villus. How is it fitted to be an absorbing 
organ? 

Structure of the small intestine. The small intestine in man 
is a slender tube nearly twenty feet in length and about one inch 
in diameter. As one of the chief functions of the small intestine 
is that of absorption, we must look for adaptations which increase 
the absorbing surface of the tube. This end is gained in part 
by the inner surface of the tube being thrown into transverse 
folds which not only retard the rapidity with which food passes 
down the intestine, but also give more absorbing surface. 

1 It is known that glycogen may also be formed in the body from protein, and 
possibly from fatty foods. 



THE VILLI 



377 



The villi. But far more important for absorption are millions 
of little projections which cover the inner surface of the small 
intestine. So numerous are these projec- 
tions that the whole surface presents a 
velvety appearance. Collectively, these 
structures are called the villi (sing, villus). 
They form the chief organs of absorption in 
the intestine, several thousand being dis- 
tributed over every square inch of surface. 
By means of the folds and the villi the 
small intestine is estimated to have an 
absorbing surface equal to twice that of 
the surface of the body. Between the villi 
are found the openings of the intestinal glands which secrete the 
intestinal juice, which contains at least one hormone and several 
enzymes with which it assists the pancreatic fluid to do its work. 




A section through the small 
intestine. What are the tiny 
projections. Of what use are 
they? 




mixed e 



Explain this section through the small intestine, giving the uses of each part. 

The internal structure of a villus is best seen in a longitudinal 
section. We find the outer wall made up of a thin layer of cells, 
the epithelial layer. These cells absorb the fluid food from withiD 



378 



HOW FOOD IS PREPARED FOR BODY USE 



the intestine. Underneath these cells lies a network of very fine 
blood vessels and in the center of the villi are spaces which, because 



thoracic duct 



Superior vena cava 



of their white ap- 
pearance after the 
absorption of fats, 
have been called 
lacteals. 

Absorption of 
foods. While diffu- 
sion and osmosis are 
important factors in 
the passage of food 
and water through 
the walls of the in- 
testine, most physi- 
ologists agree that 
the living matter in 
the cells lining the 
intestine exerts 
energy that affects 
the absorption of the 
substances that pass 
into the blood and 
lacteals. This is 
proven by the fact 
that if these cells are 
injured or poisoned, 
then absorption fol- 
lows the laws of 
osmosis and diffusion. Ordinarily the cells lining the intestine are 
like tiny chemical laboratories. Since the object of digestion is to 
furnish the cells with building material as well as energy foods, it 
is evident that amino acids, after having been absorbed into the 
blood, can get into the cells by a similar process. Fats, for example, 
in the form of fatty acids and glycerol, enter the epithelial cells of 
the villus and during the process of passing through them are 
changed back into fat particles. 




lrrnpHcxtics- 



Explain from the diagram and text how the various nutrients 
reach the blood. 



ABSORPTION OF FOOD 



379 



This fluid or lymph then passes into the lacteals and other lym- 
phatics and eventually reaches the blood. On the other hand, 
simple sugars and amino acids pass directly into the blood and 
reach the blood vessels which carry them to the liver, where, 
as we have seen, sugar is taken from the blood and stored as 
glycogen. From the liver, the food within the blood is carried to 
the heart, pumped to the lungs, returned to the heart, and is 
pumped to the tissues of the body. A large amount of water and 
some salts are also absorbed through the walls of the stomach and 
intestine. 

Large intestine. The large intestine has somewhat the same 
structure as the small intestine, except that it lacks the villi and 
has a greater diameter. Considerable absorption, however, takes 
place through its walls as the mass of food and refuse material is 
slowly pushed along by the peristaltic movements of the muscles 
within its walls. At the point where the small intestine widens 
to form the large intestine, a baglike pouch is formed. From 
one side of this pouch is given off a small tube, usually from 
one to eight inches long, closed at the lower end. This tube, the 
rudiment of what is an important part of the food tube in the 
lower vertebrates, is called the vermiform appendix. 

Practical Exercise 4. Summarize the different pathways by which food 
reaches the heart and general circulation by filling in the following table : 



Foods 


Where Absorbed 


Form 


Adaptations for 


Paths to Heart 

































Constipation. In the large intestine live billions of several 
species of bacteria which, on the whole, may be said to be useful 
because they break down and decay the indigestible parts of 
the food we have eaten. But these same bacteria in their life 
processes make and give off toxins. These substances are easily 



380 HOW FOOD IS PREPARED FOR BODY USE 

absorbed through the walls of the large intestine, and, when they 
pass into the blood, cause headaches and sometimes serious 
trouble. Hence it follows that the intestine should be emptied of 
this matter as frequently as possible, at least once a day. Con- 
stipation is one of the most serious ills the American people have 
to deal with, and it is largely brought about by the life we lead, 
with its wrong kinds of food and its lack of exercise, fresh air, 
and sleep. Fruit with meals, especially at breakfast, plenty of 
water between meals and before breakfast, and plenty of fresh 
vegetables and cereals to supply the bulk sufficient to stimulate the 
muscles of the intestine, all will aid in preventing constipation. 
Exercise, particularly of the abdominal muscles, and regular times 
for the elimination of wastes will help to correct this evil. 

Hygienic habits of eating. Any habits we may form of chewing 
our food thoroughly will aid digestion. The smaller the pieces 
of food the more surface will be presented to the digestive fluids 
containing the enzymes and the more complete will be the digestion. 
Undoubtedly much indigestion and other discomfort is due to 
hurriedly eaten meals with consequent lack of proper chewing 
of food. It is a good rule to go away from the table feeling a little 
hungry. Eating too much overtaxes the digestive organs and 
prevents their working to the best advantage. Still another 
cause of indigestion is eating when in a fatigued condition. It is 
always a good plan to rest a short time before eating, especially 
after any hard manual work. Eating between meals is condemned 
by physicians because the blood is brought to the digestive organs 
at a time when it should be more active in other parts of the body. 
The excessive use of ice cream sodas and cold drinks between 
meals is bad for this reason and because it dulls appetite for 
regular meals. 

Practical Exercise 5. 1 . Tell where each part of a meal of bread and butter, 
meat, rice pudding, and nuts is digested. 

2. Why should we chew starchy foods well before swallowing? 

3. Why is soup eaten at the beginning of a meal? (Remember it is ab- 
sorbed rapidly.) 

4. Why are partly cooked foods harder to digest than well cooked foods ? 

5. Name three easily digested foods and tell why they are easy to digest. 

6. Name three foods difficult to digest and tell the reasons why. 

7. Give, in detail, the digestion of a meal of milk, bread, and apple sauce. 



SELF-TESTING EXERCISE 



381 



TABLE OF CHEMICAL DIGESTION 






Place of Di- 


Secretion 


Enzyme 


Medium 


Substance 


End Product 


gestion 


Formed 


Contained 


Required 


Digested 


Formed 


Mouth 


Saliva 


Ptyalin 


Alkaline 


Starch 


Grape 

sugar 


Stomach 


Gastric 
juice 


Pepsin 


Acid 


Protein 


Proteoses 

and 
peptones 






Rennin 


Acid 


Casein of 
milk 


Curd 


Small 


Pancreatic 


Amylase 


Alkaline 


Starch 


Grape 


Intestine 


juice 








sugar 






Trypsin 


Alkaline 


Proteins 


Amino 

acids 






Lipase 


Alkaline 


Fats 


Fatty acid 

and 

glycerol 




Intestinal 


Erepsin 


Alkaline 


Proteoses 


Amino 




juice 






and pep- 
tones from 
stomach 


acids 






Maltase 


Alkaline 


Maltose 
(grape 
sugar) 


Glucose 






Sucrase 


Alkaline 


Cane sugar 


Glucose 






Lactase 


Alkaline 


Milk sugar 


Glucose 



Self-Testing Exercise 

Check the correct statements in your notebook : 

T. F. 1. The villi are hollow hairs which suck up digested food. 

T. F. 2. A villus absorbs food through the cells covering its surface. 

T. F. 3. The large intestine contains many bacteria which cause the 
decay of the wastes held therein. 

T. F. 4. The digestive fluids in the small intestine ultimately change 
proteins to amino acids in which form they pass into the blood. 

T. F. 5. The gastric juice changes sugar to starches. 

T. F. 6. The surface of the small intestine is increased by the villi 



382 HOW FOOD IS PREPARED FOR BODY USE 

Review Summary 

Check your knowledge of the unit by: (1) Answ ring and rechecking the 
survey questions; (2) performing the assigned exercises; (3) checking with 
the teacher your scores on the various tests and doing over those that you 
missed; and finally (4) making an outline of the unit for your notebook. 

Tests on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you 
believe are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = number of right answers X 4. 

I. The digestive tract of man (1) is a straight. tube extending from 
the mouth to the anus; (2) is the structure including the glands 
through which food passes ; (3) consists of the diaphragm, blood, and 
muscles ; (4) may be compared, part by part, with that of the frog ; 
(5) consists of the mouth (including teeth), pharynx, gullet, stomach, 
and small and large intestines. 

II. A gland (6) is a collection of cells which secrete substances 
which are of use to the body; (7) found in the stomach secretes 
saliva; (8) found emptying into the small intestine is called the 
pancreas ; (9) does its work by means of enzymes contained in its 
secretion; (10) of digestion is controlled by the nerves. 

III. Digestion (11) is necessary in order to change solid food into a 
soluble form; (12) is brought about by enzymes; (13) is principally 
brought about in the large intestine ; (14) of fats takes place in the 
small intestines ; (15) of starches takes place chiefly in the stomach. 

IV. The teeth (16) are composed chiefly of dentine; (17) are of no 
value in preparing food for digestion; (18) are divided into four 
groups on a basis of structure; (19) should be brushed frequently 
with a gritty powder; (20) if allowed to decay, can make serious 
trouble through focal infection at the base of the root. 

V. Absorption of food (21) is necessary if the cells are to get nourish- 
ment ; (22) takes place largely in the stomach ; (23) is brought about 
by the villi ; (24) takes place largely by osmosis through the cells of 
the villi ; (25) is not necessary unless we are growing, for our cells do 
not need food for other purposes. 

Achievement Test 

1. How would you make a comparison of the digestive tract of the 
frog and of man and what are the parts with the functions of each? 



USEFUL REFERENCES 



383 



2. How would you perform an experiment to show how digestion 
takes place, and what changes it brings about? 

3. What are the functions of each group of teeth ? Are your teeth 
in good condition? Have you had them looked over within six 
months? Do you brush them twice daily in the approved manner? 

4. How do you keep from having indigestion? 

Practical Problems 
Fill out the following Table : 



Glands 


Location 


Juice 


Enzymes or 
Ferments 


Action op 


Result of 
Its Action 


How Test 
for Action 









































































Useful References 

Burton-Opitz, Physiology. (W. B. Saunders Co.) 

Harrow, Glands in Health and Disease. (E. P. Dutton & Co.) 

Hunter, Laboratory Problems in Civic Biology. (American 

Company.) 
Schafer, The Endocrine Organs. (Longmans, Green & Co.) 
Starling, Principles of Human Physiology. (Lea & Febiger.) 
Wheat and Fitzpatrick, Advanced Biology. (American Book Co.) 
Williams, Anatomy and Physiology. (W. B. Saunders Co.) 



Book 




SURVEY QUESTIONS 

How does food and oxygen get to the body cells i* Why is blood from 
arteries redder than blood from veins? How is the human heart built 
and how does it work ? Why do we breathe more deeply after exercise ? 
How do we get air into the lungs ? Why do we ventilate a room ? 



UNIT XIII 



HOW ARE FOODS CIRCULATED AND USED IN THE 

BODY? 

Preview. As we have thought of the digestive system as a 
chemical laboratory, so we might think of the blood as a moving 
chemical workshop. Not only is the blood the carrier of food from 
the food tube to the cells of the body, but it also takes away the 
waste products from these same cells to those parts of the body 
that can expel them. It transports oxygen to the cells where 
oxidation takes place, and carries away the waste products of 
this oxidation. It conducts heat to all parts of the body, thus 
keeping the temperature even. The white corpuscles in the blood 
act as sanitary police, standing guard at all times to protect the 

384 



PREVIEW 385 

body in case of infection. The blood also contains substances, 
antibodies, which help combat any disease germs entering the body. 

The blood circulates through the body by means of a network 
of tubes and is controlled by the heart. Imagine a pump so 
built that it is self-regulating, so strong that it works day and 
night without rest, so powerful that it lifts several tons of weight 
the height of the body every day, year in and year out. Such is 
the human heart. Although the two sides of the heart are sepa- 
rate and distinct from each other, yet every drop of blood that 
passes through the right side of the heart also passes through the 
left side. It requires from twenty to thirty seconds for the blood 
to make a complete circuit from the ventricle back again to the 
starting point. This means that the entire volume of blood in 
the human body passes through the various organs of the body 
three or four thousand times a day. 

One of the uses of the blood in its capacity as a carrier is to 
transport certain chemical activating substances known as hor- 
mones. There are a good many such substances, the chief of which 
are manufactured by certain glands known collectively as the 
endocrines. These structures, of which the thyroid gland is a 
well-known example, have no ducts or connections with the food 
tube or other organs. Consequently their secretions can get out 
only through the medium of the blood stream. The blood dis- 
tributes the hormones to the body cells, where they cause very 
great changes to take place through their chemical actions. 

Most of us have had the experience of chopping down a tree, of 
digging a deep hole, or of lifting a heavy rock. In a very short 
time we notice that we breathe more quickly and deeply, that we 
get hot and perspire, and that after a time we become fatigued. 
What does this sequence of events mean? Evidently we can go 
back to our old analogy of the engine. To do more work we make 
a hotter fire, to get a hotter fire we increase the amount of oxygen 
that gets to the fire by regulating the draft. And we know, too, 
that if we are to keep up the fire, we must remove the ashes and 
other wastes frequently. A very similar condition exists in the 
human body. We have learned that plants and animals need 
oxygen in order to release energy, just as coal is burned to give 



386 FOODS CIRCULATED AND USED IN THE BODY 

heat to run an engine. As a draft of air is required to make a fire 
under the boiler, so, in the human body, plenty of oxygen must be 
given to the tissues so that food may be oxidized there, releasing 
energy for work and forming the wastes, carbon dioxide, water, 
and urea (nitrogen product). This oxidation takes place in all 
the cells of the body, be they portions of a muscle, a gland, or the 
brain. Here again the blood plays its part, for it carries the 
oxygen to the cells and takes away the waste products to be 
excreted either through the skin or the kidneys. The smooth 
running of this body machine of ours is only continued because 
of the exchanges of food and wastes made possible by means of 
this wonderful system of tubes and pumps which makes up the 
circulatory system. 

PROBLEM I. WHAT IS THE COMPOSITION AND WHAT ARE 
THE USES OF THE PARTS OF THE BLOOD? 

Composition of the blood. We learned in a former unit that 
the chief function of the digestive organs is to change foods so that 
they can pass into the blood. The chemical composition of the 
blood is very complex and varies in different parts of the body. 
The fluid part is the plasma, which consists of about 90 per cent 
water and the various organic food substances, digested sugars, 
fats, amino acids, mineral salts, and numerous other substances, 
among which are enzymes and hormones. The blood also holds 
three kinds of bodies : the red corpuscles, the white corpuscles, 
and the blood platelets. 

Laboratory Exercise. To study the corpuscles of the blood. Place 
a drop of frog's blood on a glass slide. Cover and examine under a 
compound microscope. What are the color and shape of the corpus- 
cles that are most numerous and most easily seen? What are the 
other irregular-shaped corpuscles, more transparent and not so easily 
seen? Are corpuscles cells? Can you prove your statement? 

Using a slide containing a drop of your own blood, note that red 
corpuscles have no nucleus. Are they cells? Do you find colorless 
corpuscles as well? How do they compare with the red in number? 
Compare the structure of blood corpuscles in man with those of a frog. 

So small and so numerous are the red corpuscles that about five 
million of them are found in a cubic millimeter of normal blood. 



COMPOSITION OF THE BLOOD 



387 








Their red color is due to an iron-protein combination called haemo- 
globin. Haemoglobin will combine chemically with oxygen, 
forming a bright red 
compound called 
oxy haemoglobin. In 
the parts of the 
body where oxida- 
tion is going on, the 
haemoglobin gives 
up its oxygen sup- 
ply. At the same 
time the plasma 

takes up the carbon dioxide which is given off by the cells. The 
result of this interchange of gases causes a change in the color 
of the blood from a dull to a bright red. 

The colorless corpuscles, of which several kinds are found in the 
blood, are irregular in outline, as they constantly change their 

form. The color- 



-kS/hite Corpuscle 
L.recC corpus-cle. 

Are the red corpuscles cells ? Explain. 



:■• 



germs 




cdtevle&s cor-jnc^de-r 



&Ls\ % 'x 






When germs or any foreign organisms enter the body, the 
colorless corpuscles, phagocytes, accumulate and either ingest 
the germs directly or with the aid of certain substances, opsonins, 
destroy them. 



less corpuscles are 
less numerous than 
the red, the ratio 
being about 1 to 
700 in a normal 
person. They in- 
crease in number 
during certain dis- 
eases. They have 
the power of move- 
ment, for they are 
found not only 
inside but also 
outside the blood 
vessels, showing 
that they have 
worked their way 
between the cells 
that form the walls 



388 FOODS CIRCULATED AND USED IN THE BODY 

of the blood tubes. Like the amoeba, the colorless corpuscles 
feed by engulfing their prey. This fact has a very important 
bearing on the relation of the corpuscles to certain diseases caused 
by bacteria within the body. If, for example, bacteria get into a 
wound, colorless corpuscles, called phagocytes (fag'6-sit), at once 
surround the spot and attack the bacteria which cause the 
inflammation. The blood contains certain antibodies called 
opsonins (6p'sS-nin), which, when present, enable the corpuscles 
to engulf and digest the bacteria. If the bacteria are few in 
number, they are quickly destroyed. If bacteria are present in 
great quantities, they may prevail and kill the phagocytes. The 
dead bodies of the phagocytes thus killed and the destroyed 
tissue help form pus which also contains many dead and living 
bacteria. When such an infection occurs, we must come to the 
aid of the colorless corpuscles by washing the wound with an 
antiseptic. 

Laboratory Exercise. What causes blood to clot ? Wash your finger 
thoroughly with soap and water. Holding the finger down, prick it 
with a sterilized needle. Draw off three drops of blood, placing each 
drop on a clean microscopic slide. Place the first slide at once on ice. 
To the second add a drop of 5 per cent sodium oxalate solution. 
Leave the third drop exposed to the air of the room. At intervals of 
one minute draw a clean hair through each drop. 

Note how long it takes the third drop of blood to clot. Compare 
this drop with the drop on ice and the drop to which the sodium oxalate 
was added. 

Laboratory Exercise. Let fresh beef blood stand over night. What 
happens ? Whip fresh beef blood briskly with an egg beater. A stringy 
almost colorless substance will stick to the beater. This, if washed care- 
fully and tested with nitric acid and ammonia, is found to contain a 
protein substance. It is called fibrin (fi'brin). 

In blood within the circulatory system of the body, the fibrin 
is held in a fluid state called fibrinogen (fi-brin'6-jen). Blood 
plasma, then, is made up of a thin liquid, serum, and of fibrinogen 
which coagulates under certain conditions, entangling the blood 
corpuscles in a network of fine threads, thus forming the clot. 

The clotting of blood is of great physiological importance, for 
otherwise we might bleed to death even from a small wound. A 
substance called thrombin is the active agent in changing fibrin- 



RELATION OF LYMPH TO THE BLOOD 



389 



TNSCC 

corpuscle. 



ogen to the insoluble fibrin of a clot. This change seems to be due 
largely to the action of minute bodies in the blood known as blood 
platelets. Under abnormal conditions these blood platelets break 
down, releasing some substances which (if the blood has the 
necessary content of calcium) cause the thrombin to do its work. 
Relation of lymph to the blood. The tissues and organs of the 
body are interlaced by a network of tubes which carry the blood. 
Outside the blood 

tubes, in spaces be- *kgf l^mph 

tween the tissue cells, 
is another fluid, much 
like plasma of the 
blood. This is the 
lymph. It is a color- 
less or yellowish 
liquid in which some 
colorless corpuscles, 
or leucocytes, are 
found. The lymph 
bathes all portions of 
the body not reached 
by the blood. It 
acts as the medium 
of exchange between 
the blood proper and 
the cells in the 
tissues of the body. 
By means of the 
food supply thus 

brought, the cells of the body are able to grow, the fluid food 
being changed to the protoplasm of the cells. By means of the 
oxygen brought by the red blood corpuscles and passed over 
through the lymph, oxidation may take place within the cells. 
Lymph not only gives food to the cells of the body, but also 
takes away carbon dioxide and other waste materials, which are 
ultimately passed out of the body by means of the lungs, skin, 
and kidneys. 

h. bio— 26 



corpuscle- fc? 




The relation of cells to the hlood. Explain exactly what 
happens in the muscle (shown in the center of the diagram) 
when it does work. 



390 FOODS CIRCULATED AND USED IN THE BODY 

Disease-resisting functions of the plasma. It is common 
knowledge that some of us " take " catching or communicable 
diseases more easily than others. Some fortunate persons are 
immune to certain diseases, that is, they do not take them, because 
certain antibodies are present in their blood. These antibodies 
act in different ways, but their work is directed against bacteria 
which get into the body and cause disease. Some antibodies, 
called lysins, have the power to dissolve bacteria. Others, called 
agglutinins, cause the bacteria in the blood to clump together in 




The diagram on the left shows free swimming typhoid bacteria. The diagram on the right 
shows the bacteria clumped together by agglutinins which are produced by the body cells as 
a protective measure. The bacteria are stationary and can be more easily destroyed by the 
white corpuscles. 



little inactive masses, so that they are an easy prey for the phago- 
cytes and lysins. We have already heard of the work of the 
opsonins, another kind of antibody. Agglutinins and certain 
other antibodies called -precipitins, which precipitate the bacteria 
from solution, have become a great help to physicians in deter- 
mining whether a person has a given disease. For example, a test 
known as the Widal (ve-daT) test is now used in all hospitals to 
determine if a person has typhoid fever. A few drops of blood 
from the patient is allowed to stand until the serum has separated. 
This is then diluted with a weak salt solution and to this are added 
some living typhoid bacteria. If the person has typhoid, the 
bacteria added to his serum will immediately become clumped 
together or agglutinated, thus showing that his antibodies are 



BLOOD TRANSFUSION 391 

already formed and at work. This is only one of a number of 
tests that have been developed in recent years. Just as each 
disease is caused by a specific kind of organism, producing a 
specific kind of toxin or poison, so the blood forms specific anti- 
bodies to fight each kind of organism or its toxins. 

Blood transfusion. It has been found that there are four types 
of human blood. About 50 per cent of all people have one type. 
After heavy losses of blood as in an accident or in an operation, 
and in some illnesses, blood is sometimes injected into a vein of 
the patient by transfusion from an artery of a donor. Before this 
operation is performed, it is necessary to make a test to see if the 
two persons have blood of the same type. This is done by means 
of the agglutinin test. Red corpuscles of the person who is to 
give the blood are added to the blood of the patient. If the red 
corpuscles are agglutinated, then the bloods are of two different 
types and transfusion cannot be made. Certain lysins called 
haemolysins may also be present in blood that will dissolve foreign 
red corpuscles of the volunteer in the blood of the patient. Tests 
may be made for these haemolysins by adding washed red cor- 
puscles of the volunteer's blood to the serum of the patient's blood. 
If the corpuscles are dissolved, this blood cannot be used for trans- 
fusion. 

Self-Testing Exercise 

Blood consists of a fluid part called (1) and three kinds of 

cells : (2) corpuscles, (3) corpuscles and (4) 

(5). Red corpuscles take up (6) by means of the 

(7) they contain. There are several kinds of (8) 

corpuscles, all of which are (9) in outline and have the 

power of (10). Those called (11) feed on bacteria 

in the blood. Blood clots because of the coagulation of the 

(12) it contains. This is brought about through the action of 

the substance (13). Plasma besides containing (14) 

contains antibodies. Among these are (15), (16), and 

(17). Lymph acts as a medium of exchange between the 

(18) and the (19) cells. Blood transfusions can be 

performed only if persons have blood of the same (20) . This 

can be found out by means of (21). 



pineal glcmct 




- -parccth/roioCs 

t>ryroid:._ 
thymus 




392 FOODS CIRCULATED AND USED IN THE BODY 

PROBLEM n. WHAT ARE THE FUNCTIONS OF SOME OF 
THE ENDOCRINE GLANDS? 

The endocrine or ductless glands and their secretions. In 

addition to all the functions already mentioned, the blood has 

another very wonder- 
ful work. We have 
already mentioned 
the hormones (from 
the Greek word hor- 
mon, meaning " to 
excite"). These 
chemical activators, 
produced by the en- 
docrine or ductless 
glands in various 
parts of the body, go 
into the blood stream, 
and stimulate another 
organ or organs in the 
body. The blood is 
the only means of 
communication be- 
tween these glands 
and the tissues on 
which their hormones 
act. Scientists are 
just beginning to ap- 
preciate the tre- 
mendous influence on 
life of some of these glands, among which are the thyroid and 
parathyroid, small glands located in the neck; the adrenals 
(ad-re'nal), tiny glands, closely attached to the kidneys; the 
pituitary body, at the base of the brain; parts of the pancreas; 
and parts of the egg-producing and sperm-producing organs, the 
ovaries and testes. The thymus and spleen, although not true 
glands, are often included with those mentioned above. 




X- f~ liver- 

^ „J-^pocncreocs 

X— -I— -spleew. 
|— occtrenccl-, 

"kidney 




The approximate positions of the endocrine glands are 
indicated in the diagram. 



ENDOCRINE GLANDS 393 

The thyroid. It has been found that undersecretion of the 
thyroid gland is responsible for the condition known as cretinism, 1 
and that this condition can be improved and frequently completely 
cured by supplying the patient with thyroid secretion, usually 
by feeding with thyroid extract. Overactivity of this gland 
produces exophthalmic 2 goiter, a condition of extreme nervousness, 
with loss of weight and other symptoms, such as protruding eye- 
balls and irregular heart action. 

In some parts of the country where the water supply comes 
from mountain sources many people are troubled with a slight 
enlargement of the thyroid gland. This trouble comes from a lack 
of iodine in the water supply. This iodine deficiency in the water 
can usually be corrected by eating foods rich in iodine, such as 
sea foods and certain vegetables, or by putting iodine in the 
drinking water. 

The adrenal glands. The adrenal glands produce a secretion, 
adrenin, which acts upon the muscles and the nervous system. 
It causes a faster beating of the heart, a heightened blood pressure, 
and other indications of increased muscular activity. It is indeed 
the emergency hormone of the body. It is this hormone that 
enables the sprinter to make his final burst of speed at the tape, 
or the football player to make a desperate stand when almost 
exhausted. It explains the " strength of desperation." Adrenin 
has been prepared in the laboratory and is known commercially 
as adrenaline (ad-re'nal-in) . It is used in medicine to contract 
the blood vessels, hasten the clotting of blood, and to strengthen 
the heart beat. 

The pituitary and thymus glands. The pituitary gland has much 
to do with body size. Dwarfs appear to lack or have very small 
pituitary glands, while giants always have abnormally large ones. 
Dr. Harvey Cushing of the Harvard Medical School, who is an 
authority on the work of the pituitary body, says : " The Lewis 
Carroll of today would have Alice nibble from a pituitary mush- 
room in her left hand and a lutein (a pigment obtained from a 

1 Cretinism (kre'tin-izm) : idiocy accompanied by physical deformity. 

2 Exophthalmic (ek'sof-thal'mik) : pertaining to a disease causing protrusion of 
eyeballs. 



394 FOODS CIRCULATED AND USED IX THE BODY 



p«::~:-:n :: The ivary in hor righ: ban 

:t:::: :irs:rr ::." 

Tar :iiyniMi. : li::Ie an iers: ■:•: :: s 
:17a:::; gland, gra iaa ly adaaoroar'S a,s ' 



pr-r-'S"-: . ;1t is i.HV 




A r;.i_: ir-e: 5| 



•an be for the most pari 



tructure found near the 
~r grow past adolescence. 
II seems to have some 
influence on the sex 
glands and on the lime 
content of bone. 

The reproductive 
glands. S :::::- par :•: 
aba — and testes 

have long been known to 
control the development 
of the so-called secondary 
sax enaaaca-rasnas ~aaea 
give us the difference 
in appearance between 
females and males. It is 
not too much to say that 
h;raz::ias are responsible 
for many sex characteris- 
ties, as experiments with 
fowls and other animals 
have proved. But popu- 

k-r S^ZeZ^ZaS oz :iir -rZ-rC: 

:: glaring zazse g.iazds 
from other animals in 
beings are greatly 

iOOZevea. 

n for many years 






zz: 



exaggerated ai 

The pancreas and liver. I: Las beez lozo^z for : 
-.Li.' :he pancreas produces sr caber secrezoz besides :haz wh 
passes into the digestive tract. But investigators have now dis- 
covered that this internal secretion, with its hormone, is produced 
in groups of cells known as the Islands of Langerhans (lang'er-hans) 
in the pancreas. If this hormone is not present, then sugar, which 
normally is stored in the Kver as glycogen, is allowed to go directly 
into the blood, where it soon appears in excessive quantities, 



CIRCULATION OF THE BLOOD 395 

causing a disease called f:Y:-":v> ;;:-:: -'; z :-: , Work by Dr. 
Banting and his co-workers o: Toronto University has resulted 
in the production of the substance insulin, which contains the 
hormone. Now :, person whose pancreas has lost the power to 
regulate the storage of glycogen in the liver may find relief through 
a proper diet and insulin in prescribed doses. 

Practical Exercise 1. Make a report on some one of the endocrine glands. 

Practical Exercise 2. Statistics show that diabetes is increasing rapidly in 

this country in spite of insulin. The reason given is the rich and heavy diet. 
What recom m endations would you make for betterment of this condition? 

Self-Testing Exercise 

Hormones are chemical (1) and are produced by 

(2) glands. Underdevelopment of the thyroid causes cretinism, 

overactivity causes (3) (4). The .... (5) 

produce the emergency hormone. The (6) gland seems to 

regulate body size. The pancreas produces a hormone which regu- 
lates the storage of (7) in the liver. If sugar goes directly 

into the blood, we have (8) and must use (9). 

PROBLEM m. HOW DOES THE BLOOD CIRCULATE 
THROUGH THE BODY? 

Circulation of the blood. The blood is the carrying agent of 
the body. Like a railroad system, it takes materials from one 
part of the human organism to another. Tins it does by means 
of the organs of circulation, — the heart and blood vessels. These 
blood vessels are of three kinds: the <:•:-/■;'-/>. elastic muscular 
tubes, which carry blood away from the heart; the :-;.':<. Thin- 
walled vessels containing valves which bring the blood back to 
heart : and the capillaries, which connect the smallest arteries 
with the smallest veins. The organs of circulation thus form a 
system of connected tubes through which the blood flows. 

Demonstration 1. What is the structure of the heart ? Refer to the 
diagram of the heart, with the arteries and veins connected with it. 
Where do the chief arteries lead to and from where do the large veins 
come? Obtain the heart of a recently killed steer and examine it. not- 
ing the four chambers, the valves, and the blood tubes le:\ r : 



396 FOODS CIRCULATED AND USED IN THE BODY 



from it. The upper chambers are called the right and left auricles 
respectively ; the lower chambers, the right and left ventricles. Which 
have the thicker walls? What is probably the use of these walls? 

Notice the position of the valves and the direction of their move- 
ment. In what direction do arteries lead? Veins? 

Do the chambers all connect with one another? Write a paragraph 
describing the structure of the heart. 

The structure of the heart. The heart is a cone-shaped mus- 
cular organ about the size of the fist. It is surrounded by a loose 



artery to right lung-i 
vein 



right 
auricle 



right 
ventricle. 



vein. 




,artery to 



ery to 
le/ft lurng 



__, veins from 
lurigs 



left 
_- auricle 



left 
..ventricle^ 



.aor-toc 



How does the blood get from the left ventricle to the right ventricle ? 

membranous bag called the pericardium, the inner lining of which 
secretes a fluid in which the heart lies. If we should cut open the 
heart of a mammal down the midline, we could divide it into a 
right and a left side, each of which has within the heart no connec- 
tion with the other side. 

Practical Exercise 3. To make an apparatus that will demonstrate the fact 
that the heart is a double force pump. 

The heart in action. The heart is constructed on the same 
plan as a force pump, the valves preventing the reflux of blood 
into the auricles when it is forced out of the ventricles. Blood 
enters the auricles from the veins because the muscles of that part 
of the heart relax; this allows the space within the auricles to 



THE COURSE OF THE BLOOD IN THE BODY 397 



fill. Almost immediately the muscles of the ventricles relax, thus 
allowing blood to pass into the chambers within the ventricles. 
Then, after a short pause, during which time the muscles of the 
heart are resting, a wave of muscular contraction begins in the 
auricles and ends in the ventricles, with a sudden strong contrac- 
tion which forces the 
blood out into the ar- 
teries. Blood is kept 
from flowing backward 
by the valves, which 
act in the same manner 
as do the valves in a 
pump. The blood is 
thus made to pass into 
the arteries upon the 
contraction of the ven- 
tricle walls. 

Practical Exercise 4. 

Why is the heart a force 
pump? Why is the heart 
said to be double? 

The course of the 
blood in the body. 
There are two distinct 
systems of circulation 
in the body. The 
pulmonary circulation 

takes the blood through the right auricle and ventricle, to the 
lungs, and passes it back to the left auricle. This is a relatively 
short circulation, in which the blood receives oxygen in the lungs 
and gives up carbon dioxide. The longer circulation is known as 
the systemic circulation; in this system, the blood leaves the left 
ventricle through the great dorsal artery called the aorta. Through 
ever-branching arteries blood passes to the muscles, the nervous 
system, kidneys, skin, and other organs of the body. It gives 
up food and oxygen in these tissues, receives the waste products 
of oxidation while passing through the microscopic tubes, capil- 
laries, and returns to the right auricle through veins which join 





Explain how the heart is a force pump. 



398 FOODS CIRCULATED AND USED IN THE BODY 

and increase in size until they form two large vessels known as 
the venae cavae. 

Portal circulation. Some of the blood, on its way to the heart, 
passes to the walls of the food tube and to its glands. From these 
parts it is sent with its load of absorbed food to the liver. Here 
the vein which carries the blood (called the portal vein) breaks up 
into capillaries around the cells of the liver, which takes out the 
excess sugar and stores it as glycogen. From the liver, the blood 
passes directly to the right auricle. The portal circulation con- 
nects the stomach and the small intestine with the liver. It is 
the only part of the circulatory system where the blood passes 
through two sets of capillaries on its way from auricle to auricle. 

Demonstration 2. To show circulation in the web of a frog's foot. 

Examine under a compound microscope the web of the foot of a living 
frog. Note the network of tiny blood vessels, capillaries. Those 
vessels in which the blood moves in spurts are tiny arterioles; the 
larger vessels in which the blood moves slowly or steadily are veins. 

Structure of the arteries, veins, and capillaries. A distinct 
difference in structure exists between the arteries and the veins in 
the human body. The arteries, because of the greater strain 
received from the blood which is pumped from the heart, have 
thicker muscular walls, and in addition are very elastic. Veins 
are much thinner-walled than arteries and have small valves which 




1. 1... 

2 - 2... 

3 3... 



lepitbelial.-- 
layer 

.2. smooth ... 
muscle 
tissue 



2>.Connectr 
"tisstxe 




I epitheliia 



Capillary 



Explain the difference between an artery, a vein, and a capillary. 



BLOOD PRESSURE 



399 



open in the direction of the blood flow. Capillaries are a net- 
work of very thin-walled vessels through which food, oxygen, and 
colorless corpuscles pass out to the tissues. 

The pulse and blood pressure. The pulse is caused by the 
contraction of the ventricle which causes a wave of distention to 
travel along the blood vessel. This pulse can easily be felt in the 
larger arteries that are near the surface of the body. As the blood 
is forced from the heart into the arteries it comes under pressure 
caused by the resistance given to the flow of blood by the small 
capillaries. Thus a definite blood pressure is caused, which is 
seen when we cut an artery. Blood pressure can easily be meas- 
ured by an instrument called the sphygmomanometer. 

Practical Exercise 5. Visit a physician and have him explain what happens 
when he takes your blood pressure, and the significance of what he finds. 

Lymph vessels. The lymph is collected from the various tissues 
of the body by ducts provided, like the veins, with valves. The 
pressure of the blood within the blood vessels continually forces 
more plasma into the lymph ; thus a slow current is maintained 
from the lymph spaces into lymph tubes. On its course the lymph 
passes through many lymph glands, where impurities appear to 
be removed. The lymph ultimately passes into a large tube, the 
thoracic (thS-ras'ik) duct, and empties into the blood stream in the 
neck region. 







Explain, with reference to your text, why it is that blood flows in one direction in the veins. 



400 FOODS CIRCULATED AND USED IN THE BODY 



The lacteals. We have already learned that part of the digested 
food (chiefly sugars, amino acids, salts, and water) is absorbed 

directly into the blood through the 
walls of the villi and carried to the 
liver. Fat, however, is passed into 
the spaces in the central part of 
the villus known as the lacteals. 
This fluid or lymph then passes 
from the lacteals into other lym- 
phatics, and eventually drains into 
the blood system by way of the 
thoracic duct. Shortly after a 
meal the lacteals are filled with a 
white fatty substance, but at other 
times they are filled with a fluid 
very similar to the lymph in the 
other lymphatics. 

Laboratory Exercise. What is the 
effect of exercise on the heartbeat ? 

Place the middle finger of the right 
hand two inches from the ball of the 
thumb, to locate the pulse. Count the 
number of beats per minute. The 
normal rate in men is seventy-two 
beats per minute ; in women, seventy- 
six. It is higher in children. 

Then under the direction of a 
leader, take a hard setting-up drill 
for three minutes with the windows 
open. Count the pulse beats as be- 
fore and tabulate the result. Note 
any difference in respiration. 

What effect did the exercise have 
on the rate of the heartbeat? Can 
you explain the reason? • Can you 
explain the difference in the rate of 
Diagram of the circulatory system. The respiration? Show in your table the 
l^J^^^^h^JT'h^ difference between the normal pulse 

those containing venous blood are blue, . . , . . F 

and the lymphatics are yellow. and the one taken after exercising. 

The effect of exercise on the circulation. Exercise in modera- 
tion is of undoubted value, because it sends more blood to parts 




TREATMENT OF CUTS AND BRUJSES 



401 






of the body where increased oxidation is taking place as the 
result of the exercise. The best forms of exercise are those which 
give work to as many muscles as possible — walking, out-of-door 
sports, any exercise that is not violent. Exercise should not be 
attempted immediately after eating, as this causes a withdrawal of 
blood from the digestive tract to the muscles of the body. Neither 
should exercise be continued after becoming tired, as poisons are 
then formed in the muscles, which cause the feeling we call fatigue. 
Overdoing in any sport or game is dangerous. Fatigue is a signal 
to rest. Remember that extra work given to the heart by extreme 
exercise may injure it, causing possible trouble with the valves. 
Older people and those who through excessive use of stimulants 
or tobacco or other causes have developed arteriosclerosis, 1 
hardening of the arteries, need to be especially careful. " A man 
is as young as his arteries," because the hardening of the wall 
raises the blood pressure, and if 
the inelastic artery wall breaks, 
due to overexercise, death may 
result through apoplexy. 

Treatment of cuts and bruises. 
Blood which oozes slowly from a 
cut will usually stop flowing by 
the natural means of the forma- 
tion of a clot. A cut or bruise 
should, however, be washed in a 
weak solution of lysol or some 
other antiseptic in order to pre- 
vent bacteria from obtaining a 
foothold on the exposed flesh. 
If blood gushes from a wound, in 
distinct pulsations, an artery has 
been severed. A tight bandage 
known as a tourniquet (toor'ni-ket) 

must be tied between the cut and the heart, If a vein is cut, the 
blood flows smoothly. In this case, a tourniquet is applied on the 
side of the cut away from the heart. 

1 Arteriosclerosis : ar-te'ri-6-skle-ro'sis. 




What kind of blood vessel has been cut? 



402 FOODS CIRCULATED AND USED IN THE BODY 

Laboratory Exercise. What methods should be used to stop the 
flow of blood in case of an accident ? Decide first whether the blood is 
issuing from an artery or from a vein. How would you know? Then 
apply a tourniquet made from a stick or ruler and a handkerchief or 
towel, using a stone or knife to press down on the blood vessel. 

Imagine an artery severed in the arm below the elbow and practice 
applying a tourniquet there. Apply a tourniquet, if the artery cut is 
above elbow. Does the pulse in the wrist stop when the tourniquet is 
applied ? Explain reason. 

Conclusion. How would j r ou make a tourniquet? Describe fully. 
Where must a tourniquet be placed when an arteiy is cut? Where 
when a vein is severed ? What is the use of the tourniquet ? 

The effect of alcohol upon the blood. Alcohol, when taken 
habitually, causes several very serious effects upon the blood and 
blood vessels. The bodily resistance against disease which is 
brought about by the presence of specific antibodies is greatly 
weakened in those who use alcohol to excess. Drinking also has 
an injurious effect upon the colorless corpuscles, as it lowers their 
ability to fight disease germs. Place a drop of alcohol on a slide 
containing active amoebas, if 3 r ou wish to see the effect on a similar 
type of cell Alcohol acts on the nerve centers controlling the 
heart and blood vessels. Alcohol may even, in cases of long and 
severe drinking, cause changes to take place in the walls of the 
blood vessels which may result in the breaking of the vessel or the 
formation of a blood clot in the vessel. Such an injury in blood 
vessels in the brain causes apoplexy and often results in sudden 
death. 

Self-Testing Exercise 

The circulation of the blood is brought about by a heart which acts 

as a ........ (1) (2). Blood passes out from the heart 

through (3), then into the tissues by means of the (4), 

returning to the heart again by way of the (5). There are 

two important systems of circulation in the body : the (6) to 

and from the lungs, and the (7) which leaves the heart from 

the (8) ventricle and passes out to all the body organs. 

Arteries are (9) and (10), capillaries are very 

(11), and veins have (12) walls and have 

(13) to keep the blood from running backward. The pulse is caused 
by the gushing of blood from the (14), when the walls of the 



THE ORGANS OF RESPIRATION IN MAN 



403 



(15) contracts. Blood pressure is caused by the (16) 



of the tiny 
(18). 



. (17) against the blood forced from the 



PROBLEM IV. WHAT IS RESPIRATION? 






Laboratory Exercise. A comparison of the respiratory tract of a 
frog and a mammal. Open a frog's mouth and find the slitlike open- 
ing (glottis) just back of the tongue. Insert a blowpipe or a glass tube 
and blow down the short windpipe (trachea) which branches into two 
divisions leading to the lungs (bronchial tubes). What happens to the 
lungs ? 

Examine a section cut through a frog's lung. Is it hollow? Now 
compare the baglike lungs of the frog with the more complicated lungs 
of man (see diagram). Do you find the same structures leading to 
the lungs of man? (Read your text.) Which part of the lungs of 
man would be elastic ? Which part of the frog's ? Why? 

If blood vessels were found in the walls of these sacs, what gas might 
be brought in the 

blood to this point? • / ^%|i(i& 

What gas might be lai^ri^^A„f8j| 

in the air? How Sricebc* Rj.iJ 

might the exchange t 3 

of these gases take trach«r...i. ,-J 

place ? Where might windpipe b; 

it take place ? 

The organs of 
respiration in man. 
We have noted the 
fact that the lungs 
are the organs which 
give oxygen to the 
blood and take from 
it carbon dioxide. 
Air passes through 
the nostrils into the 
windpipe. This 
cartilaginous tube, 
the top of which 
may easily be felt 
as -the Adam's apple 

of the throat, divides into two bronchi (bron'ki). The bronchi 
within the lungs break up into a great number of smaller 




air- 5Yxc 
bronchial 



The tissue is cut away from one of the lungs to show the air 
tubes. Trace the course of air from the nose to the air sacs. 



404 FOODS CIRCULATED AND USED IX THE BODY 

bronchial tubes, which divide somewhat like the small branches 
of a tree. The bronchial tubes are lined with ciliated cells, the 
cilia of which are constantly in motion. They lash with a 
quick stroke toward the outer end of the tube, that is, toward 
the mouth. Hence any foreign material in the tubes will be 
raised first by the action of the cilia and then by coughing or 
" clearing the throat." The bronchial tubes end in very minute 
air sacs, little pouches having elastic walls, into which air is 
taken when we inspire, or take a deep breath. In the walls 
of these pouches are numerous capillaries. Through the very 
thin walls of the air sacs a diffusion of gases takes place, which 
results in the blood giving up carbon dioxide and taking up oxygen. 
As a result of this process the color of the blood becomes a brighter 
red, due to the combination of the oxygen with the haemoglobin 
in the red corpuscle. 

Demonstration 3. To determine changes that take place in the air 
in the lungs. 

Breathe on the bulb of a thermometer and record any changes. 
Breathe gently on any glass or polished metal surface. Xote what 
happens. Take a moderate breath, and force air (tidal ah) by means 
of a glass tube through lirnewater. Xotice what occurs. Force the 
last part of a deep expiration (reserve air) through lirnewater. Xote 
result. 

Thrust a lighted splinter into a bottle of air. How long does it 
burn? Xow fill a glass jar with expired air by the downward displace- 
ment of water. Invert the jar, keeping it covered. Remove the 
cover, and introduce into the jar a lighted wood splinter. How long 
does it continue to burn? What does this indicate? Why? (Air 
loses about one fourth of its oxygen while in the lungs.) 

What are the changes that take place in blood in the lungs ? What 
does air gain in the lungs ? What does it lose ? What is one reason 
for deep breathing? 

Composition of Fresh Am and of Am Expired from the Lungs 



Constituents 


In Outdoor Air 


Ix Air Expired 

FROM THE LUXGS 


Oxygen 

Carbon dioxide 

Xitrogen and other gases . . 
Water vapor 


20.96 
.04 
79. 
variable 


16.4 
4.1 
79. 
.5 



CELL RESPIRATION 



405 



As the table shows, there is a loss of nearly 5 per cent of oxygen, 
and a corresponding gain in carbon dioxide and water vapor, in 
expired air. There are also some organic waste substances in 
expired air which are not shown in the table. 

Cell respiration. It has been shown, in the case of very simple 
animals, such as the Paramecium, that when oxidation of food 
takes place in the cell, energy will result. In man the oxygen 
taken into the lungs 
is not used there, 
but is carried by 
the blood to all 
parts of the body 
where work is done. 
Cell activity de- 
mands food and 
oxygen. 

When oxidation 
of food takes place 
in the cell, energy is 

released for cell work and certain wastes are formed. The waste, 
carbon dioxide, is given off to the blood when any food containing 
carbon is burned. When proteins are burned, other wastes con- 
taining nitrogen are formed. These must be passed off from the 
cells, as they are poisons. This is done by the lymph and the 
blood, which take the waste materials to points where they may be 
excreted or passed out of the body. Water, another waste product, 
is excreted by the skin and kidneys. 




Explain this diagram. 



Self-Testing Exercise 

An (1) of oxygen and (2) (3) takes place 

in the blood as it passes through the (4) (5) of 

the lungs. Air entering the lungs has about (6) per cent 

more (7) than expired air. Respiration takes place in th& 

. . .' (8) of the body. As a result of cell activity after (9) 

and (10) are taken into the cell (IP (12), 

(13) and (14) wastes are given off. 

h. bio — 27 



406 FOODS CIRCULATED AND USED IN THE BODY 



PROBLEM V. WHAT ARE THE MECHANICS OF BREATHING? 

Demonstration 4. To show the mechanics of breathing. 

Pass a glass Y tube through a rubber stopper. Fasten two small toy- 
balloons to the branches of the tube. Put the stopper in the small 
end of a bell jar. Adjust the tube so that the balloons hang free 

in the jar. Attach a 
string to the middle of a 
piece of sheet rubber. 
Tie the rubber over the 
large end of the jar. 

To what structures in 
our bodies may the bal- 
loons and rubber sheet be 
compared? Pull down 
the string gently. What 
effect does the lowering 
of the sheet rubber have 
on the balloon? Why? 
Push the rubber into the 
bell jar to form an arch. 
What happens to the 
balloons? Why? Ex- 
plain how this experi- 
ment may be compared 
to breathing? 





Spinal 
Coitxmn 



lung 
Cavity 

^diaphrag 




The pleura. The 
lungs are inclosed in a 
thin, elastic, membra- 
nous sac, the pleura. 
This membrane is com- 
posed of moisfc tissue. 
In breathing, when the 
lungs become larger, the smooth, moist surface of the pleura 
prevents the friction that otherwise would occur between the 
lung and the walls of the chest. 

The mechanics of breathing. In every breath there are two 
-movements, inspiration (taking air in) and expiration (forcing air 
out). An inspiration is produced by the contraction of muscles 
between the ribs, together with the contraction of the diaphragm, 
the muscular wall forming the floor of the chest cavity; this 
results in pulling the diaphragm down and pulling the ribs up- 
ward and outward, thus increasing the space within the chest 



COMMON DISEASES OF THE NOSE AND THROAT 407 



cavity for the air to rush in. Then the diaphragm relaxes and 
rises and the muscles between the ribs relax. This pressure forces 
the air out of the lungs, thus producing expiration. During these 
processes an exchange of oxygen in the air and of carbon dioxide 
in the blood takes place. 

Practical Exercise 6. Explain the difference between breathing and respi- 
ration. 

Hygienic habits of breathing. Every one ought to accustom 
himself to inspire slowly and deeply in the open air. A slow 
expiration should follow. Take care to force all the air out. 
Breathe through the 
nose to warm the in- 
spired air before it 
enters the lungs. Re- 
peat this exercise 
several times every 
day. This will prevent 
certain of the air sacs, 
otherwise used only in- 
frequently, from be- 
coming hardened and 
permanently closed. 
Deep breathing should 
become a habit with 
growing girls and 
boys. It can best be 
practiced with win- 
dows open, after rising 
in the morning 
just before retiring at 
night. 

Common diseases of the nose and throat. Catarrh is a dis- 
ease to which many people with sensitive mucous membrane of 
the nose and throat are subject. It is indicated by the constant 
secretion of mucus from this membrane. Chronic catarrh should 
be attended to by a physician. Often we find children breathing 
entirely through the mouth because the air passages in the nose 




^KJcu.in., 



Diagram showing the capacity of the lungs. The tidal air 
is that taken in an ordinary breath. Complemental air is 
and that taken in a very long breath. In a forced expiration we 
can expel from 75 to 100 cubic inches of reserve air. What 
is left in the lungs is residual air. 



408 FOODS CIRCULATED AND USED IN THE BODY 

are closed. If this condition continues for any length of time, the 
nose and throat should be examined by a physician for adenoids, 
growths of soft masses of tissue which fill up the nose cavity and 
prevent normal breathing. Many a child, backward at school, 
thin and irritable, has been changed to a health}', normal child, 
by the removal of adenoids. Sometimes the tonsils, at the back 
of the mouth cavity, become diseased and enlarged, causing 
serious throat troubles and sometimes acute rheumatism and 
heart disease. 

Relation to health. We all know that exercise in moderation 
has a beneficial effect upon the human organism. Exercise, 
besides training the muscles, increases the activity of the heart 
and lungs, causing deeper breathing and giving the heart muscles 
increased work ; it liberates heat and carbon dioxide from the 
tissues where the work is taking place, thus increasing the respi- 
ration of the tissues themselves, and aids mechanically in the 
removal of wastes from tissues. Exercise is of immense impor- 
tance to the nervous system as a means of rest. 

Demonstration 5. To show the prone-pressure method of artificial 
respiration. 

Place the person face downward with his head turned to the side 
and supported on his arm. Kneel astride him at the bend of his 
knees and slowly but strongly press down and forward with the 
hands, keeping the arms straight, immediately over the lower part of 
the chest cavity. Hold this pressure for about three seconds and 
then swing the weight of the body off suddenly, thus allowing the 
lungs of the subject to fill with ah. After two seconds repeat the 
pressure as before. Count the seconds as you perform this operation 
so as to make the total number of respiratory movements twelve 
to the minute. 

Why time these movements twelve to the minute? "Why press 
down on the ribs? vThat structures play a part when this is done? 

Suffocation and artificial respiration. Suffocation results when 
the supply of oxygen is shut off from the lungs. It may be brought 
about by an obstruction in the windpipe, by a lack of oxygen in 
the air, due to inhaling some other gas in quantity, by drowning, 
or from a severe electric shock. In any one of the above cases, the 
person's life may be saved by prompt recourse to artificial respira- 
tion. The prone-pressure method is considered one of the best. 









BEST METHODS OF VENTILATION 409 

Do not give up work if the patient does not at once show signs 
of recovery. Persons who have been under water for some time 
have been resuscitated after four to five hours' work. Prompt, 
regular, and continued effort is the thing that counts. 

Self-Testing Exercise 

In breathing there are two movements, (1) and (2). 

In the first movement the (3) are pulled up and outwards, 

and the (4) is lowered, thus making a larger space within the 

chest cavity into which (5) may pass (6) is a pas- 
sive movement, the air being forced out by the return of the (7) 

and (8) to their former positions. We inspire about 

(9) times a minute. About (10) (11) inches of air are 

taken into the lungs during a " long " breath. To perform artificial 
respiration by the prone-pressure method we place the patient face 

(12), kneel astride him, and slowly but strongly press 

(13) and (14) just over lower part of the (15) 

(16) at a rate of (17) times a minute. Keep this 

pressure up for (18) seconds, release suddenly, rest (19) 

seconds, and repeat. 

PROBLEM VI. WHAT ARE THE REASONS FOR, AND THE 
BEST METHODS OF VENTILATION? 

Demonstration 6. To show methods of ventilating rooms. 

Make a grooved box 8 X 10 inches at base, 8 inches high, with 
sliding glass door. Place on side and have 4 half-inch holes, two at 
top and two at bottom, bored in each end and fitted with corks. 
Place three candles in the box. Light the candles. 

With all the corks in place, how long (take exact time) do the candles 
burn? 

Remove the upper corks from both ends. How long do the candles 
burn? 

Remove the lower corks. How long do the candles burn? 

Remove the upper and lower cork from one end. How long do 
the candles burn? Remove the upper corks from one end and the 
lower ones from the opposite end. How long do the candles burn? 

Make cross-section sketches and explain the different trials. Use 
dotted lines and arrows to represent the course of the air. 

What is the best method of ventilating a room ? Why should people 
sleep with windows open? Make a diagram to show how to ventilate 
a -room. How would you ventilate through a window without making 
a draft? Can you explain the school system of ventilation? 



410 FOODS CIRCULATED AND USED IN THE BODY 

Need of ventilation. We have all experienced a certain dis- 
comfort in a crowded auditorium or schoolroom after a short time. 
Some people think that this discomfort is caused by lack of oxygen 
in the air or by the presence of too much carbon dioxide. But 
experiments conducted by the New York State Ventilation Com- 
mission and in many laboratories have shown that this discomfort 
comes largely from two sources, the rise in temperature and the 
increase in humidity in the air. The source of this heat and 
moisture is largely the bodies of the people who are in the room. 

In order to get rid of excess moisture, reduce the heat, and 
remove the other products of respiration from the air, ventilation 
is necessary. Ventilation is defined as adequate replacement of 
used air with fresh air. In addition, air in buildings contains dust, 
with its load of bacteria, odors of various kinds, and sometimes 
poisonous gases. 

Methods of ventilation. Since 1800 to 3000 cubic feet of air 
are needed by the average person each hour, various devices 
for changing the air in rooms are used. In schools, fresh air 
is often drawn in by fans, washed to remove dust and bacteria, 
and then forced through ducts into the rooms, the used air in the 
room passing out through other ducts. But recent studies in- 
dicate that much of the expensive equipment of school buildings 
might be discarded in favor of window ventilation top and bottom 
with boards placed so as to prevent drafts. 

Practical Exercise 7. Make a survey of the temperature conditions in your 
own school. Take hourly temperature records in several different rooms. 
Make the report cover at least one week. 

A temperature of not more than 68° F. is most favorable for 
mental work. It is found that during the winter, when artificial 
heat is used, the air becomes too dry. Various devices are used 
to evaporate moisture in a room and raise the humidity content 
of the air somewhat, but no effective device is in general use for 
keeping the humidity equal to that of the outside air. Conse- 
quently, when we go from a warm, dry room into the cool, out- 
of-door air, the skin becomes chilled and we may take cold. One 
of the best ways we can keep the air in our rooms moist is to place 
pans of water on registers or radiators. 



VENTILATION OF SLEEPING ROOMS 



411 



Ventilation of sleeping rooms. Sleeping in badly ventilated 
rooms is frequently the cause of much discomfort and often of 
illness. Windows should be open top and bottom, but no direct 
draft should be allowed. 
This ventilation may 
often be managed with 
the use of screens. 

In cities especially, 
the night air is purer 
than day air, because the 
factories have stopped 
work, the dust has 
settled, and fewer people 
are on the streets. The 
old myth of " night air" 
being injurious has long 

since been exploded, and thousands of people of delicate health, 
especially those who have weak throats or lungs, are regaining 
health by sleeping out of doors or with the windows wide open. 
The only essential in sleeping out of doors is that the body be 
kept warm and the head be protected from strong drafts. 




Is this a good method of window ventilation? Why? 



Self-Testing Exekcise 
Ventilation is the (1) of (2) air with 



(3) 



air. From (4) to (5) cubic feet of air are needed in 

a room by every person per hour. Sleeping rooms are best venti- 
lated by opening the window (6) and (7), but a 

(8) should be avoided. Ventilate the lungs by (9) 

(10). 



PROBLEM VII. WHAT ARE THE ORGANS OF EXCRETION 
AND HOW DO THEY FUNCTION? 

Laboratory Exercise. The structure of the kidney. Some idea of 
the internal structure of the kidney of man may be gained by examina- 
tion of a sheep's kidney. Get the butcher to leave the mass of fat 
around the kidney. What is the use of this fat? Notice, after re- 
moving the fat, that the kidney appears to be closely wrapped in a 
thin coat of connective tissue ; this is called the capsule. 



412 FOODS CIRCULATED AND USED IN THE BODY 



Remove the kidney from this capsule. Notice its color and shape. 
The depression called the hilum is deeper than the corresponding region 
in a kidney bean. The hollow tube passing out from this region is 
called the ureter. Blood vessels also enter and leave the kidney at 
the hilum. 

Cut the kidney lengthwise into halves. Try to find the following 
regions : (1) the outer or cortical region (note its color) ; (2) the inner 
or medullary layer (this layer is provided with little projections, which 
are the pyramids of Malpighi, so called after their discoverer, Marcello 
Malpighi, a celebrated Italian physiologist) ; (3) the cavity or pelvis 
of the kidney. At the summit of each pyramid is a small opening 
through which escapes into the pelvis the secretion formed in the little 

tubules, which make up the pyra- 
mids, and in which the real work 
of excretion is performed. 

Where is the waste taken from 
the blood in the kidney ? Where 
does this waste pass out of the 
body? 

Organs of excretion. All the 

life processes which take place 
in a living thing result ulti- 
mately, not only in the giving 
off of carbon dioxide, but also 
in the formation of organic 
wastes within the body. The 
retention of the wastes which 
contain nitrogen is harmful to 
animals. In man, the skin and 
kidneys remove these wastes 
from the body, hence they are 
called the organs of excretion. 

The human kidneys, like 
those of the sheep, are com- 
posed of masses of excretory 
tubules. The outer end of 

The organs of excretion. Note the blood supply h f thege tubules ultimately 

to the kidneys. Of what use is the bladder? u 

opens into the pelvis, the space 
within the* kidney ; the inner end forms a tiny closed sac. In 
each sac, the outer wall of the tube has grown inward and carried 
with it a very tiny artery. This artery breaks up into a mass of 




urethra 



WASTES GIVEN OFF BY THE BLOOD 



413 



artery vein. 






capillaries, which, in turn, unite to form a small vein as they 
leave the little sac. Each of these sacs contains a number of 
blood vessels, the glomerulus 
(glSmer 'dolus). 

Wastes given off by the 
blood in the kidney. In the 
glomeruli the blood loses by 
osmosis, through the very thin 
walls of the capillaries, first, a 
considerable amount of water 
(amounting to nearly three 
pints daily) ; second, a nitrog- 
enous waste material known 
as urea; third, salts and other 
waste organic substances. 
These waste products pass 




topalvif 
of kidn^ 

Each kidney is composed of a large number 

mtO tne pelVIS 01 tne Kidney of long tubules. The blood flows through the 

flnH thrrmo-h Hiif»t<? nrptpr* glomeruli (mass of blood capillaries) and then 

ana tnrOUgU aUCIS, Ureters, through the capiUaries surrounding the tubules, 

into the bladder. Wastes from the blood pass through the walls 

_,. . . of the blood-vessels (glomeruli) into the tubules, 

The Waste products from which lead to the bladder. 

the kidney, together with the 

water containing them, are known as urine. Urine normally con- 
sists of about 96 per cent water and 4 per cent dissolved solids. 
The total amount of nitrogenous waste leaving the body each day, 
by means of the kidneys, is about twenty grams. After the blood 
has gone through the glomeruli of the kidneys it is purer than in 
any other place in the body, because it has lost much of its nitrog- 
enous waste in them and before going to them it gave up a large 
part of its carbon dioxide in the lungs. So dependent is the body 
upon the excretion of its poisonous material that in cases where 
the kidneys do not do their work properly, death may ensue 
within a few hours. Since the blood which passes through the 
kidneys is being continually depleted of water, one should drink 
plenty of water to make good this loss. 

Diet plays a very important part in the care of the kidneys. If 
we' overbalance our diet with too much protein food, we throw 
increased work on these organs. The nitrogen in proteins cannot 



414 FOODS CIRCULATED AND USED IN THE BODY 



be oxidized, so, combined with other elements into urea and 
other wastes, it is eliminated through the kidneys. 

Laboratory Exercise. To study the skin as an organ of excretion 
and of heat control. Examine the diagram of a cross section of skin. 
Locate the epidermis, dermis, sweat glands, oil glands, nerves, and 
blood vessels. 

Examine the surface of your skin with a hand lens. Where is the 
epidermis and what structures does it contain? What structures 
are found in the dermis ? 

Insert your hand in a clean, dry fruit jar. Wrap a towel over the 
opening of the jar so as to allow no air to get in between your hand 
and the sides of the jar. What happens in the jar? What is given 
off from the hand? 

Weigh yourself. Note the weight. Exercise violently for half an 
hour. Weigh yourself again. Note the weight. Was there any 
change in weight? How must the change of weight have been 
brought about ? Remember that when oxidation of food or tissue takes 

f place in the body, three prod- 



at least, 




organic 



are formed : 
wastes, and 



anct 



ucts, 
heat, 
water. 

(Food + oxygen = carbon 
dioxide + water + organic 
wastes + heat + muscular 
energy.) 

Take the temperature of 
the body before and after 
exercise by placing a clinical 
thermometer in the mouth. 
Account for any change in 
temperature. 

What three substances are 
given off from human bodies 
that might affect the air of 
a closed room? Are you 
more comfortable on a hot 
humid day or on a hot dry 
day? Explain. 



The skin as an organ of 
excretion. We have already 
learned that the skin is an 
organ of protection. Let 
us now see how it aids in 
excretion. The glands already studied form the excretion known 
as perspiration, a watery solution containing little carbon dioxide, 



A sweat gland. Explain, with reference to the text, 
where the water that is given off comes from. The 
waste materials. 



COLDS AND FEVERS 415 

urea, and some salts (common salt among others). The com- 
bined secretions from these glands amount normally to a little 
over a pint during twenty-four hours. At all times a small amount 
' of perspiration is given off, but this is evaporated or is absorbed 
by the underwear. Since this passes off unnoticed, it is called 
insensible perspiration. 

Regulation of the heat of the body. The body temperature of 
a person engaged in manual labor will be found to be but little 
higher than the temperature of the same person at rest. The 
muscles, equal to nearly one half the weight of the body, release 
about five sixths of their energy as heat. At all times they are 
giving up some heat. The temperature of the body is largely 
regulated by the activity of the sweat glands. The blood carries 
much of the heat, liberated in the various parts of the body by the 
oxidation of food, to the surface of the body, where it is lost in 
the evaporation of sweat. In hot weather the blood vessels of 
the skin are dilated ; in cold weather they are made smaller by the 
action of the nervous system. The blood thus loses water in 
the skin, and as the water evaporates, we are cooled off. The 
object of increased perspiration, then, is to remove heat from the 
body. With a large amount of blood present in the skin, per- 
spiration is increased; with a small amount, it is diminished. 
Hence, we have in the skin an automatic regulator of body tem- 
perature. 

Practical Exercise 8. Why is the amount of perspiration noticeably in- 
creased in hot weather and after doing hard work? 

Colds and fevers. The regulation of blood passing through 
the blood vessels is under control of the nervous system. If this 
mechanism is interfered with in any way, as for example through 
bacterial toxins released in the body, the sweat glands may not 
do their work, perspiration may be stopped, and the heat from 
oxidation held within the body. The body temperature goes up, 
and a fever results. 

If the blood vessels in the skin are suddenly cooled when full of 
blood, they contract and send the blood elsewhere. As a result an 
increase of blood in the internal organs or a congestion may follow. 




416 FOODS CIRCULATED AND USED IN THE BODY 

Colds are, in reality, a congestion of membranes lining certain 

parts of the body, as the nose, throat, windpipe, or lungs, together 

r ,. _. „ . . with a growth of bacteria 

l ,;,^^.^ ,:;„:.^,;,^, ^,::^^ .; ' ;, : which were present in the* 
■ga? @ 9 % <L @ © @ @^ *9y-» mouth or throat. Some colds 

^ @ \^K& are commuincaD l e an( i gain 

=^«^^^© # f/^ entrance to the body when 

^-^TT^fc -. ; the resistance is low. 

J @ © @ © @ © f ®j®®£ fS*" When SUfferln S fr0m a C0ld -" 

™' "'"" " " it is therefore important not 

_____ to chill the skin, as a full 

§|l%8yfiv blood supply should be kept 

j*$W. m in it and thus kept from the 

'jfp^ seat of the congestion. For 

£ this reason hot baths (which 

:vn©^|®rtlle brin & tne blood to the skin), 
^^^^^ the avoiding of drafts (which 
chill the skin), and warm 

Explain this diagram. What has happened in lxl _. r i r j. 

the lower figure? clothing are useful factors m 

the care of colds. Very im- 
portant also are rest in bed, fresh air, plenty of water to drink, 
and free bowel movements. 

Practical Exercise 9. What is a congestion and how is it caused ? How do 
we " take cold "? Is there more than one kind of cold? 

Self-Testing Exercise 

Body temperature is regulated by action of nerves in the (1). 

They either cause the small blood vessels to (2) or (3), 

thus placing more or less (4) at the (5) of the body 

where the (6) heat may be (7) by perspiration. The 

kidneys are organs of (8) (9) waste is passed out 

as (10). An oversupply of (11) food may make too 

much work for the kidneys. 

Review Summary 

Test your knowledge of the unit by: (1) rechecking the summary ques- 
tions ; (2) performing all the assigned exercises ; (3) checking with the teacher 
on all tests and trying over the parts you missed ; (4) and finally making an 
outline of the unit for your notebook. 



TESTS 417 

Test of Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you believe 
are true. In another column under INCORRECT write numbers of untrue statements. Your 
grade = right answers X 2. 

I. The blood contains (1) fluid food in its plasma; (2) red and 
colorless corpuscles ; (3) haemoglobin in its white corpuscles ; (4) en- 
zymes and hormones ; (5) a substance called fibrinogen, which acts in 
causing the blood to clot. 

II. Blood is necessary for the body because (6) it acts as a medium 
of exchange between the body cells and the source of their food supply ; 
(7) it contains regulative substances called vitamins ; (8) it acts as a 
carrier for the chemical activators called hormones ; (9) only through 
the blood is oxygen carried to the cells and carbon dioxide carried 
away; (10) it carries waste materials away from the cells. 

III. Antibodies (11) help to make us immune to diseases caused 
by bacteria; (12) called lysins can dissolve bacteria; (13) called 
agglutinins cause bacteria to stick together ; (14) are specific and 
fight specific toxins ; (15) are made use of in the Widal Test. 

IV. The endocrine glands (16) are the salivary, gastric, and 
intestinal ; (17) are those glands which have no ducts ; (18) include 
the thyroid, parathyroid, thymus, adrenal, the pituitary, and parts of 
the pancreas, the ovaries, and testes ; (19) such as the adrenals may 
increase body activity: (20) such as the pituitary probably control 
growth in the body. 

V. The blood circulates (21) because it is alive; (22) because the 
heart acts as a force pump ; (23) because arteries and veins are con- 
nected by capillaries ; (24) through the body cells ; (25) to all the cells 
in the body. 

VI. The lungs (26) are the chief organs of excretion in the human 
body ; (27) are organs for the exchange of oxygen and carbon dioxide ; 
(28) are masses of tiny air sacs, which are thin walled and covered with 
capillaries; (29) are made larger or smaller during the process of 
breathing; (30) take in oxygen and give off water, carbon dioxide, 
some organic wastes, and heat. 

VII. Respiration (31) is a process by which oxygen reaches the 
body cells and carbon dioxide is removed from them; (32) is the 
same as expiration and inspiration ; (33) takes place in body cells ; 
(34) and breathing mean the same thing; (35) is raising and lower- 
ing the ribs and diaphragm. 



418 FOODS CIRCULATED AXD USED IX THE BODY 

VIII. Ventilation (36) is necessary in order to raise the temperature 
of a room; (37) removes carbon dioxide and renews oxygen; (3S) is 
necessary because moving ah' helps to keep a room more comfortable : 
(39) removes moisture, heat, carbon dioxide, and other products of 
respiration and renews the supply of oxygen : ^40) is best brought 
about in sleeping rooms by having the windows open top and bottom. 

IX. Body wastes are removed (41) from the cells by the blood 
which carries the organic wastes to the kidneys : (42) from the kidneys 

in the form of urea : (43) in a gaseous state : 44; from the body by 
the kidneys: (45) best by taking cathartics. 

X. The skin (46) regulates body heat : (47) furnishes protection 
against germ- : 4 8 is an organ of excretion : (49) contains millions 
of sweat glands under nervous control ; (50) should be kept warm if 
one has a cold, for this keeps blood from the internal organs and thus 
prevents congestion. 



Achievement Test 

1. What do blood corpuscles look like under the compound micro- 
scope ? 

2. How would you demonstrate the capillary circulation in the web 
of the frog's foot ? 

3. How would you make a tourniquet and what would you do 
in case of an accident where loss of blood occurs? 

4. Why is blood transfusion not possible between some people and 
possible between others ? 

5. What are the endocrine glands and what is the function of 
each? 

6. How could you make a diagram of circulation of blood in your 
own body? 

7. How can you prove that you oxidize materials (food or tissues"' 
in your own body'? 

8. How can you demonstrate the prone-pressure method of arti- 
ficial respiration? 

9. How can you demonstrate the best method of ventilating a 
room and show why it is the best method? Do you practice this in 
your sleeping room ? 

10. How could you demonstrate the changes that take place in 
air in vour lungs ? 



USEFUL REFERENCES 



419 



Practical Problems 
1. Fill out the following table : 

WASTES OF THE HUMAN BODY 



Waste 


Whebe Fokmed 


How Excreted 


Organs Used in 
Process 











2. Fill out the table below as completely as you can : 



Part of Blood 


Substance or Structure 


Functions 









Useful References 

Broadhurst, How We Resist Disease. Chapter V-VII inc. (J. B. Lippin- 

cottCo. 1923.) 
Burton-Opitz, Textbook of Physiology. (W. B. Saunders Co. 1925.) 
Fisher and Fisk, How to Live. Chapter IV. (Funk & Wagnalls Co. 

1925.) 
Harrow, Glands in Health and Disease. (E. P. Dutton & Co. 1922.) 
Hunter, Laboratory Problems in Civic Biology. Pp. 139-152 inc. 

(American Book Company.) 
Kimber and Gray, Textbook of Anatomy and Physiology. Pp. 184- 

298. (The Macmillan Co. 1926.) 
Martin, The Human Body, Advanced Courses. (Henry Holt & Co. 

1926.) 
Sharp, Foundation of Health. (Lea & Febiger. 1924.) 




SURVEY QUESTIONS 

What do we mean by the term behavior ? By what things or forces may 
plants and animals be affected ? What are your sense organs ? What are 
the parts of your nervous system ? What is an instinctive act ? What is 
a habit ? How and why can man control things in his environment ? 



Wide World Photo 



UNIT XIV 



HOW HAS MAN BECOME THE CONQUEROR OF THE 

WORLD? 

Preview. We have seen many instances in which plants and 
animals respond to stimuli. In our study of plants we found 
examples of responses to light, gravity, and moisture. These 
simple responses are called tropisms. But if we are asked to 
explain why these responses took place, we can only say that 
protoplasm exhibits the power of irritability by means of which 
the organism is preserved from injuries and can obtain from its 
environment the materials needed to carry on its life processes. 

The reactions of a dog to the sound of his master's voice or to 
the odor of a piece of meat seem to be quite a different matter 

420 



PREVIEW 421 

from these simple responses. However, biologists and psychol- 
ogists agree that it is only carrying a little further this matter of 
response to a stimuli: It is held by some people that most of 
our everyday actions, of which we do not think, are due to reac- 
tions to certain stimuli. Most of the acts which we perform 
during a day's work are the results of the automatic working of 
various parts of our body. The heart pumps the blood which 
circulates its load of food, oxygen, and wastes ; the movements 
of breathing are performed; the kidneys and skin discharge the 
wastes from the body; and the nerves carry messages to and 
from the brain. These many complicated acts go on every day 
within the body and are seemingly undirected, but they are in 
reality under the control of the autonomic nervous system. 

On the other hand, the body may also be influenced by what 
goes on around it. Our entire day at school may be colored by 
what happened at the breakfast table. Or suppose we oversleep, 
eat our breakfast hastily, run to school, reaching there a few 
minutes late, and therefore are marked tardy. This sequence 
of events will influence our entire day. The digestive glands 
in the stomach have not been properly stimulated, due to our 
hastily eaten breakfast. Certain internal secretions of the glands, 
poured into the blood when we ran to school and when we were 
declared late, might arouse our emotions, and cause us to do and 
say many things for which we would probably be sorry later. 
All of the actions were really initiated through changes in our 
environment. The fact that we overslept made breakfast later, 
our hurry made school seem further away, the closed door gave 
us a decided jolt and changed the smooth running of our nervous 
machine. So conditions do modify our life activities. 

Most of our activities are habits ; that is, we have learned to 
do them so well that we can now do them without thinking. 
Habits may be broken, but to do this we must become conscious 
of them, and earnestly try to break them. Either we shall become 
slaves to habits or habits will serve us. That is the thing that 
every person should realize while still in high school. Later, good 
habits cannot be acquired or bad habits cannot be broken so easily 
and one will eventually become conquered by his habits. 
h. bio — 28 



422 MAN BECOMES THE CONQUEROR OF THE WORLD 



PROBLEM I. WHAT ARE THE CHIEF RESPONSES OF 
PLANTS AND ANIMALS? 

Demonstration 1. To show some tropisms in plants and animals. 

Grow some bean seedlings in a glass dish which is kept watered at 
one side only. Grow some bean seedlings in unequal illumination. 
Examine oxalis or clover at night and in the morning, in order to ob- 
serve " sleep " movements of leaves. Touch a leaf of a sensitive plant 
with a pencil. 

Place Euglena in a vessel with unequal light illumination. 

In the first two cases, note the arrangement of roots against the 
glass side of the dish. What leaf movements of oxalis and sensitive 
plant are noticeable? Where in the vessel do you find Euglena most 
abundant? 

What forces act upon plants and animals? How do they affect 
them? 

How plants and animals receive stimuli. In the simplest 
plant and animal cells which live by themselves there are no 

specialized parts which are es- 
pecially fitted to receive out- 
side stimuli. The amoeba, for 
example, is influenced by 
temperature, food, and other 
stimuli, but it has no sense 
organs. Some tiny plant-like 
animals (or animal-like plants) 
such as Euglena (ti-gle'nd) have 
a tiny structure called an eye- 
spot, which seems to be more 
sensitive to light than other 
parts of the cell. 
The more complex single- 
cWoroplosti-g ^ „/l cytoplasm celled animals, as Paramecia, 

have parts of the cell (cilia) 
more sensitive to touch than 
other parts. Animals and, to 

Euglena. Would you call it a plant or an ani- a lesser degree, plants, as they 
mal ? Give your reasons. , i . , . 

become more complex in struc- 
ture, tend to have special parts set aside to receive stimuli. These 
special parts of complex animals are called sense organs. 



flccgelluTn. 

moxjcfh 

gUllet— 

contrctdtiW 

vacuole/ 

nucleus. I&* 



.eyes pot 




RESPONSES OF THE PLANT 423 

Responses of plants and animals. The responses which plants 
and animals make to certain definite stimuli are called tropisms. 
Such responses may be either positive or negative, and appear 
to be mechanical behaviors. They may be listed as follows : 
Phototropism or response to light 
Geotropism or response to gravity 
Plants Hydrotropism or response to water 

and < Thigmotropism or response to contact 
Animals Chemotropism or response to chemical substances 
Thermotropism or response to temperature changes 
. Galvanotropism or response to electricity 
Animal / R neo ^ r °pi sm or response to water currents 

I Anemotropism or response to air currents 
The response of roots to gravity, the growth of stems toward the 
source of light, the opening of some flowers in the daytime and 
others only at night, the climbing of plants by means of tendrils or 
other organs stimulated by touch, are a few of the many examples 
which might be mentioned. 

Practical Exercise 1. Make a list of all tropisms that you have ever seen 
plants or animals exhibit. 

Some parts of the plant are more sensitive. While a plant 
as a whole is sensitive to stimuli of different kinds, it is certain that 
some parts are more sensitive than others. For example, experi- 
ments show that in the root an area of not more than one milli- 
meter in length is most sensitive to gravity, as the turning response 
takes place there. Some tips of stems show a similar sensitive- 
ness, and so do certain parts of growing leaves. 

Self-Testing Exekcise 

Check in your workbook the correct statements : 

T. F. 1. The tip of the root responds most readily to gravity. 

T. F. 2. Euglena has an eyespot which is sensitive to light. 

T. F. 3. Geotropism is response to the stimulus of gravity. 

T. F. 4. Phototropism is response to the stimulus of chemical sub- 
stances. 

T. F. 5. Rheotropism is response to water current. 



424 MAN BECOMES THE CONQUEROR OF THE WORLD 

T. F. 6. The amoeba has no special organs of sense. 

T. F. 7. If touched, the leaves of sensitive plants show thermo- 
tropism. 

T. F. 8. The responses of simple animals to stimuli are always 
positive. 



PROBLEM II. HOW DO SIMPLE PLANTS AND ANIMALS 
RESPOND TO STIMULI? 

Demonstration 2. To show the use of the pulvinus to a plant,. 

Stain a longitudinal section of a bean stem to show the pulvinus. 1 
What might be the use of it ? How is it able to do that ? 

The mechanism of responses in plants. Some of the results 
of responses are easily seen in plants, but the method by which 
the responses are brought about is not so easy to see. For example, 
we say leaves place themselves so as to get as much light as possible. 

But this movement is different 
from that found in animals 
which have an internal skele- 
ton with muscles attached. 
The changes in position in 
parts of plants are often pro- 
duced by a more rapid growth 
of the cells on one side of a 
structure than on the other, 
this growth having been ex- 
cited by an external stimulus, 
such as gravity, water, light, 
or heat. Such are the curving 
movements of roots or stems. 
The turning of the leaves in a horizontal position is brought about 
by the more rapid growth of tissues on one side of the leaf stalk 
than the other. 

Changes in the position of leaves are often brought about by 
special structures at the base of the petiole, as may be seen in the 
bean plant. These structures, called pulvini 1 (sing, pulvinus), 

1 Pulvinus (pul-vTn#s) : cushionlike enlargement of petiole at its point of inser- 
tion qn the sterol 




Clover leaf. (1) In the morning. (2) In the 
evening. Explain the difference. 



RESPONSES OF THE SIMPLEST ANIMALS 



425 



contain thin- walled cells filled with water, and the position of the 
leaf probably depends on the relative amount of water in these 
cells. The more rapid movements of the opening and closing of 
flower petals ; the changes in position of leaflets of the pea, clover, 
alfalfa, oxalis, and 
other plants at night 
and in the morning; 
and the relatively 
rapid response of the 
leaves of the sensitive 
plant to outside stimuli 
are all explained by 
changes in the water 
content of the cells in 
the pulvini, or by rapid 
and temporary fluc- 
tuations in growth on 

Opposite Sides Of the Whatis thepulvinus? 

leaves, or by a combination of both. But other than external 
stimuli may influence and modify the growth and actions of plants. 
We know that enzymes play an important part in the storage of 
food in fruits and seeds, and there seem to be evidences of vitamin 
and hormone action as well. It is probable that the protoplasm 
of a plant is under much the same control as is the protoplasm of 
an animal. 




What use is it to a leaf ? 



Demonstration 3. To show responses of Paramecium. 

Place a drop of Paramecia culture in a grooved slide. At intervals, 
heat the water at one end of the slide by introducing a hot needle into 
it. Note the actions of the Paramecium as the water becomes warmer. 
Single out one Paramecium and make a diagram showing exactly how 
it gets away from the heated area. This reaction is known as the 
" avoiding reaction." How does a Paramecium escape from an 
unfavorable environment ? 



Responses of the simplest animals. We have already seen 
that amoebas and Paramecia seem to respond to the presence of 
food. Examination of a drop of hay infusion containing Para- 
mecia will show many collected around masses of food, indicating 



426 MAN BECOMES THE CONQUEROR OF THE WORLD 



If obstacle 



1 



that they are attracted by it. In another part of the slide we may 
find a number of the Paramecia lying close to the edge of an air 
bubble, with the greatest possible amount of their surface exposed 
to its surface. These animals are evidently taking in oxygen by 
diffusion. They are breathing. A careful inspection of the jar 
containing Paramecia shows thousands of tiny whitish bodies 
collected near the surface of the jar. Some force or forces keep 
them close to the surface. Professor Jennings and others have 

made careful studies of the reactions of 
Paramecia and other one-celled animals 
to various stimuli, and have found that 
in general they react positively toward 
\***^ favorable and negatively toward un- 

favorable conditions in their environ- 
ment. For example, if a slide contain- 
ing Paramecia is heated at one side, 
the animals will back off from the un- 
favorable stimulus, then shoot forward 
until they encounter the heat, then 
again back off and repeat the opera- 
tion until they escape from the heated 
area. 

This method of escape from the un- 
favorable environment is called the 
method of trial and error. It is an ex- 
ample of the way in which some of the 
lower organisms react to the unfavor- 
able conditions of their environment. 
If by such methods they do not es- 
cape from harmful conditions, they 
perish. 

Different intensities of light, different kinds of light, the passage 
of a current of electricity through the water, different chemical 
substances placed in the water, as well as many other factors, cause 
very definite responses on the part of these one-celled organisms. 
The responses in general save the organism from harm, or help 
it, and thus may be said to be adaptive responses. 




;4- 



£ 



%' 



: H>~; 



Trial and error method of a Para- 
mecium. Explain what has hap- 
pened, using the figures as guides. 



SENSE ORGANS AND WHAT THEY DO 427 

Self-Testing Exercise 

Changes in the (1) of leaves are brought about by a 

structure called the (2). Paramecia react (3) to 

a favorable environment and (4) to an unfavorable one. 

Paramecia can be observed to (o) to the presence of 

(6), (7) and (8). If Paramecia cannot escape 

from (9) conditions, they die. Plants change their positions 

in response to such stimuli as (11), (12), 

(13), and (14). 

PROBLEM HI. WHAT ARE SENSE ORGANS AND WHAT DO 

THEY DO? 

Demonstration 4. To show types of sensory structure in certain 
animals. 

Materials. Insects with different types of antennae. Crustaceans 
with antennae and antennules. Grasshoppers, with wings removed to 
show tympanic membrane. Model of vertebrate eye and ear. Living 
crickets, earthworms, crayfish, and living goldfish. Food, such as 
apple or meat. Weak acetic acid. 

Method. Arrange preserved specimens and models so that they 
may be passed around in class or observed on the demonstration table. 
Living material should be placed in pans or aquariums where they 
can be fed, and stimulated with weak acid. 

Note the hairs projecting from the antennae and antennules of the 
insects and crustaceans. They are sensory in nature. Note in the 
grasshopper the sensory organ, which receives sound. Study the 
model of the human ear. Does our ear do more than receive sound? 
Study the model of the human eye. Compare it with a camera. 

Observe carefully what happens when food, such as a bit of apple, 
is placed in a dish containing live crickets or earthworms. Note also 
what happens when crayfish or goldfish are fed meat. How do they 
become aware of the presence of food ? 

Place some cotton soaked in weak acid close to anterior end of an 
insect, a worm, and a crayfish. What happens? 

How do animals become aware of food or harmful substances ? 

Sense organs and what they do. Most plants do not react 
quickly to stimuli, because they have no special sense organs. 
Nor have the one-celled animals any special part of the cell fitted 
to receive stimuli. But in animals composed of numerous cells, 
division of labor soon appears, and we have organs fitted to receive 
light stimuli (eyes), touch stimuli (tactile hairs, etc.), and sound 



428 MAN BECOMES THE CONQUEROR OF THE WORLD 




The fine hairs of the appendages of the lobster 
are organs of touch and they make the animal 
sensitive to its surroundings. 



stimuli (sensory hairs, tympana of insects, and the ears of higher 
animals). These end organs or structures at the outside of the 
animal, when connected by nerves to organs of movement, like 
muscles, bring about reactions to stimuli which result in obtaining 

food, in escaping from ene- 
mies, and in many other im- 
portant functions. 

Some examples of sense 
organs. One of the simplest 
sense organs is a sensory hair 
which contains nerve cells. 
These cells have become 
modified, so that when they 
are stimulated they send a 
message inward to another 
kind of nerve cell in the cen- 
tral part of the body. This 
cell in turn sends a message 
which stimulates a muscle to 
work, and the animal's body is involuntarily moved either away 
from or toward the source of the stimulus. This type of response 
is known as a simple reflex. 

There are many kinds of sensory structures in the lower animals. 
The antennae of insects are for feeling and for receiving odors and, 
in some insects, sound waves. A few insects like the locust have 
tympanums, or ears. In some animals the " ear " assists in bal- 
ancing while in other animals the ear is an organ of hearing as 
well as for balancing. In the. shrimp, the " ear " is a tiny pit, 
the wall of which is lined with sensory hairs. In this pit are small 
grains of sand or other substances, which move about as the animal 
changes its position, and thus assist in making the animal aware 
of its position in space. A German named Kreidl (kri'd'l) showed 
in an experiment that shrimps, after molting, place small grains 
of sand in their statocysts (stat'6-sists) or balancing pits. He kept 
the shrimps in an aquarium containing small particles of iron which 
the shrimps took in place of sand. Using a magnet, Kreidl then 
found that its pull against gravity affected the shrimps as did the 



HOW IS MAN'S BODY CONTROLLED? 



429 



force of gravity when sand grains were in the statocysts. This 
showed that the statocysts are balancing organs. 

Light-receiving devices are of various kinds, from the simple 
eyespot in Euglena or small groups of sensory cells to the com- 
plicated compound eye of insects and the camera-like structure 
of man's eye. 

Practical Exercise 2. Fill in the following table, listing the various kinds 
of sensory structures found in each animal you have studied. 



AXIMAL 


Structure 


Where Found 


How Used 












- 















Self-Testing Exercise 

In higher animals, (1) from special structures carry 

(2) to organs of movement which bring about (3). When an 

animal (4) moves away or toward the (5), the re- 
sponse is a (6) . Light-receiving devices vary from the 

(7) in (8) to the (9) (10) in man. 



PROBLEM IV. HOW IS MAN'S BODY CONTROLLED? 

Laboratory Exercise. The anatomy of the nervous system. In a 

frog from which the organs of the body cavity have been removed, 
note the white glistening cords (nerves) which seem to come from 
under the backbone. Follow the course of some of the larger nerves. 
To where do they lead? Now turn the frog over and with sharp 
scissors and a scalpel remove very carefully the bony covering (the 
skull) from the whitish body (the brain). 

How many parts appear to be in the brain? Notice the white 
elongated hemisphere of the forebrain or cerebrum. 1 The two anterior 
projections of the cerebrum are called olfactory lobes. Where do these 
lobes seem to lead ? What do you think, from the name, their use is ? 

Just back of the cerebrum, find two large lobes, known as optic 
lobes, which have to do with sight. Look at the chart. Are the eyes 
connected with the optic lobes? Back of the optic lobe we find the 
cerebellum 2 and medulla, 3 the latter running directly into the spinal 
cord, from which rise the spinal nerves you have noted. 



Cerebrum : ser'e-brum. 



2 Cerebellum : ser'e-beTwm. 



Medulla: me-dul'a. 



430 MAN BECOMES THE CONQUEROR OF THE WORLD 

Compare, part by part, the brain of the frog with a model of the brain 
of man. In what respect is a frog's nervous system like that of man? 
How does it differ? Write a description, comparing the nervous sys- 
tem of the frog with your own, using charts and models as a guide. 





The sense organs of man. We have seen that simpler forms 
of life perform certain acts because outside forces acting upon 
them cause them to react. All many-celled animals, including 
man, are put in touch with their surroundings by what we call 

special sense organs. The senses of 
man, besides those we commonly 
know as sight, hearing, taste, smell, 
and touch, are those of temperature, 
pressure, and pain. It is obvious that 
such organs, to be of use, must be at 
the outside of the body. Thus we 
find eyes and ears in the head, and 
taste cells in the mouth, cells in the 
nose for smelling, and others in the 
skin which are sensitive to heat or 
cold, pressure or pain. 

The nervous system. In the ver- 
tebrate animals, including man, the 
nervous system consists of two divisions. One, including the 
brain, spinal cord, and nerves, makes up the central nervous 
system. The other division, called the autonomic nervous system, 
consists of small collections of nerve cells called ganglia. These 
ganglia are mostly included in two chains parallel to the spinal 
cord. This system transmits stimuli from the central nervous 
system to the heart, glands, and muscles of the internal organs. 

Strangely enough, we do not see with our eyes or taste with 
our taste cells. These organs receive the stimulations which are 
sent inward by means of a complicated system of greatly elongated 
cell structures, until the sensory message reaches an inner station, 
in the central nervous system. We see and hear and smell in our 
brains. 

Neurons. The unit of structure of the nervous tissue is a cell, 
called a neuron. It is a mass of protoplasm containing a nucleus. 



Some parts of the body are more 
sensitive to certain stimuli than are 
others. The diagram on the left 
shows an organ that is concerned in 
the sensation of touch; the one on 
the right, concerned in the sensation 
of pressure. 



NEURONS 



431 






protective 
sYiecctli- 



The body of the nerve cell is usually irregular in shape, and differs 
from other cells by possessing several delicate, branched, proto- 
plasmic projections called dendrites. One of these processes, the 
axon, is much longer than the others and ends in a muscle or in a 
network of endings around another nerve cell. It is not certain that 
these two nerve cells are actually in u 

contact, but a stimulus is transmitted 
from one cell to the other by means 
of this network. Such a communica- 
tion is called a synapse (si-naps'). 
The axon forms the pathway over 
which nervous impulses travel to and 
from the nerve centers. _ 

A nerve consists of a bundle of 
tiny axons, bound together by con- 
nective tissue. As a nerve ganglion 
is a center of activity in the nervous 
system, so a cell body is a center 
of activity of the neuron and may 
send an impulse over the thin strand 
of protoplasm (the axon) prolonged 
many hundreds of thousands of times 
the length of the cell body. Some 
neurons in the human body, although 
visible only under the compound 
microscope, give rise to axons several 
feet in length. 

Because some axons originate in 
organs that receive stimuli and send 
them to the central nervous system, 
they are called sensory axons. Other axons originate in the central 
nervous system and pass outward, producing movement of muscles. 
These are called motor axons. The neurons possessing these axons 
are either sensory or motor neurons. When neurons connect sen- 
sory with motor neurons they are called associative neurons. 

Reflexes and their place in our lives. We have seen that 
reflexes play a very important part in the responsive life of simple 




terminal .branches 

A neuron. Where might such a cell 
be found? Where might the termi- 
nal branches be ? 



432 MAN BECOMES THE CONQUEROR OF THE WORLD 




A reflex arc. Explain this diagram. 



animals. They are equally important in our own lives. The 
involuntary brushing of a fly from the face, or the attempt to 

move away from 
■cell bocix the source of an- 

noyance when 
tickled with a 
feather, are exam- 
ples of reflexes. 
In a reflex act, a 
person does not 
think before act- 
ing. The nervous 
impulse comes 
from the outside 
sensory cells to motor cells in the spinal cord, or in the cerebellum, 
the lower part of the brain. The message is short-circuited back 
to the surface by motor nerves, without ever having reached the 
thinking centers. 

Practical Exercise 3. Make a list of all the reflex acts that you have made 
during the past twenty-four hours. Approximately what proportion of your 
actions are reflexes ? 

The brain of man. In man, the central nervous system con- 
sists of a brain and spinal cord inclosed in a bony case. From the 
brain, twelve pairs of nerves are given off ; thirty-one pairs more 
leave the spinal cord. The brain has three divisions. The 
cerebrum makes up the largest part. In this respect it differs 
from the cerebrum of the frog and lower vertebrates. It is divided 
into two lobes, the hemispheres, which are connected with each 
other by a broad band of nerve fibers. The outer surface of the 
cerebrum is gray. It shows many convolutions or folds which give 
a large surface. The cell bodies and synapses of the neurons are 
found in this part of the cerebrum. Holding the cell bodies and 
fibers in place is a kind of connective tissue. The inner part 
(white in color) is composed largely of nerve fibers which pass to 
other parts of the brain and down into the spinal cord. Below 
the cerebrum lies a smaller portion of the brain, the cerebellum. 
The two sides of the cerebellum are connected by a band of nerve 



PARTS OF THE NERVOUS SYSTEM 



433 



fibers, the pons, which run around into the lower part of the brain 
or medulla oblongata. The medulla is the enlarged beginning of 
the spinal cord, and is made up largely of fibers running longi- 
tudinally. 

Functions of parts of the central nervous system of the frog. 
From studies of lower animals scientists have learned about the 
functions of various parts of the central nervous system in man. 

It has been found that if the entire brain of a frog is destroyed 
or separated from the spinal cord, the frog will continue to live. 
It will not move or croak, but if acid is placed upon the skin the 
legs will make movements to push away and to clean off the irritat- 
ing substance. The spinal cord is thus shown to be a center of 
defensive movements. If the cerebrum is separated from the 
rest of the nervous system, the frog seems to act a little differently 
from the normal animal It jumps when touched, and swims when 
placed in water. It will croak when stroked, or swallow if food 
is placed in its mouth. But it manifests neither hunger nor fear, 
and is in every sense a machine which will perform certain actions 
after certain stimulations. Its movements are automatic. The 
cerebellum and medulla then must be the centers of muscular 
coordination and automatic or involuntary movements. If we 




olfactory.! ; 
lobes tef 

cerebral I- 

optic 

lobeslr 



cerebeflu 
medulla K 

K spinal 
cord 




optic 

-Jlobes 



cerebalV 
medulla} 

spinal 
Cord 




....... olfactory lobes.. 

cerebral lobes.. 



optic. 
lobes 
medulla 




cerefcell 

■medulla- 



Spinal cow- rjf spinal cord 




Brains of a perch, frog, alligator, pigeon, and cat. Can you tell, from diagrams, why a cat has 
more intelligence than a pigeon or a fish ? 

watch the movements of a frog which has the brain uninjured in any- 
way, we find that it acts spontaneously. It tries to escape when 
caught. It feels hungry and seeks food. It acts like a normal frog 
This shows that the cerebrum is the center of all voluntary activities. 



434 MAN BECOMES THE CONQUEROR OF THE WORLD 



auditory' 
araoc ^ 



motor areec 

s&nsory area 



thinking*, 
abstract, 
concentrati 




thinking" 
learning^ and, 
understSmdiiTg- 

— Cerebrum 
visual area 

.Cerebellum 

- medulla 
^coordination 



According to the observations of physicians and the experi- 
mentations of scientists certain functions are thought to be 
controlled by different portions of the brain. 



Localization of functions. In a general way, our central 
nervous system is like that of the frog. The autonomic activi- 
ties are largely con- 
trolled outside the 
brain. The cerebel- 
lum and spinal cord 
take care of the ha- 
bitual reflexes which 
we learned when 
growing into child- 
hood. The cerebrum 
has to do with a large 
number of conscious 
activities. 

A large part of the 
area of the outer 
layer of the cerebrum 
seems to be given over to some one of the different functions of 
hearing, sight, touch, and movements of body parts. The move- 
ment of the smallest part of the body appears to have its definite 
localized center in the cerebrum. In addition, certain areas have 
to do with association and memory; that is, the cells store 
memories of past acts or things. Those areas have to do with 
our voluntary actions, for the stored memories are really stored 
sensory impressions. Voluntary acts, then, are the completion of 
reflexes. Even reasoning may be explained as the association of 
concepts, the relation of which is not close. Reasoning is per- 
ceiving relationships in seemingly unrelated facts. 

Functions of the nervous system of man. There are several 
types of activities over which the nervous system has control. 
The first are the so-called autonomic activities of the body. The 
heart beats and we breathe when we are asleep as well as when 
we are awake. Our glands emit secretions and our kidney cells 
excrete wastes, all without any consciousness on our part. 

A second kind of function is the kind of activity which once 
was learned but now has become " second nature " or habitual. 
If we have well-regulated body machines, we get up in the morning, 



FUNCTIONS OF NERVOUS SYSTEM 435 

automatically wash, clean our teeth, dress, go to the toilet, eat 
our breakfast, walk to school, and even perform such complicated 
processes as that of writing, without thinking about or directing 
the machine. Certain acts which once we learned consciously 
have become automatic. 

Early in our lives we begin to gain a higher control of our body 
activities. We then make conscious choice; we weigh one course 
of action against another and decide which is the best course for 
us to follow — in short, we think. This is the highest type of 
conscious activity. 

Through the sense organs the nervous system keeps us in touch 
with the outside world. 

Self-Testing Exercise 

Check the correct statements in your workbook : 

T. F. 1. Man's body is controlled by his brain. 
T. F. 2. A neuron is a nerve cell. 

T. F. 3. The autonomic nervous system regulates functions which 
are beyond our control. 

We see and hear in our brain. 

Sensory nerves send outgoing messages. 

Motor nerves send messages toward the central nervous 

The human brain consists of convolutions, hemispheres, 
and thirty-one pairs of nerves. 

T. F. 8. There are three types of functions over which the human 
brain has control : the autonomic, activities such as the beating of the 
heart, or secreting of glands ; the habitual ; and those having to do 
with conscious thought processes. 

T. F. 9. The cerebellum controls our conscious activities. 

T. F. 10. More of our daily actions are voluntary than habitual. 

PROBLEM V. WHAT PART DO THE SENSE ORGANS PLAY 
IN THE CONTROL OF THE BODY? 

Laboratory Exercise. Blindfold a pupil. Then lightly touch the 
back of his hand with the two points of the dividers. Begin with 
them close together and gradually move them apart. Have the 
blindfolded person tell as soon as he feels the two points separately. 



T.F. 


4. 


T.F. 


5. 


T.F. 


6. 


system. 




T.F. 


7. 



436 MAN BECOMES THE CONQUEROR OF THE WORLD 

Experiment further on various parts of the body, and record the re- 
sults in the form of a table. 





Place Touched 


Distance between Points 


Back of Hand . . 






Palm of Hand . . 






Finger Tips . . . 






Wrist . ' . . . . 






Upper Arm . . . 






Back of Neck . . 






Back 







Which part of the body seemed most sensitive to touch ? 

Laboratory Exercise. With a ruler and a pen, draw a square inch 
on the underside of your wrist. Heat a wire nail until it feels 
very hot. Now lightly touch all parts of the skin within the square 
area. Do all parts feel the heat, or only the sense of slight pressure 
of the nail? Mark with a little cross all spots that are sensitive to 
heat. 

Xow cool off the nail by placing it on ice. Wipe it dry and apply 
while still cold in the same way to the area marked off on the wrist. 
Do you feel the sensation of cold in all spots? Mark as before, this 
time using a dot. 

Do all parts of the skin feel heat and cold? What does this mean? 

Laboratory Exercise. What is the relation between taste and smell ? 

Cover your eyes and hold your nose tightly with the fingers. 
Have another pupil place on your tongue very small pieces of peeled 
apple, peeled raw potato, peeled raw turnip, and onion. Have the 
pieces exactly the same taste? Have some one record the results. 
Are you aware of the different flavors ? Are you aware of them with 
the nostrils open? Try the experiment with a number of other sub- 
stances, as sugar, vinegar, vanilla, mustard, salt, and spices. 

Rub the tongue dry. Place a little sugar on it. In what condition 
must materials be in order to be tasted ? 

In tabular form note those substances which are recognized by 
taste only and those which are recognized by taste and smell. 



TASTE 



437 





Recognized by Taste 


Recognized by Taste and Smell 


Apple .... 




• 


Onion .... 






Potato .... 






Turnip .... 






Salt 






Sugar .... 






Mustard . . . 






Vanilla .... 






Vinegar .... 

1 







What is the relation of taste and smell in distinguishing flavors ? 

Taste. The surface of the tongue is folded into a number of 
little projections known as papillae (pd-pil'e). In the folds 
between these projections, 
near the root of the tongue, 
are located the organs of 
taste. These organs are 
called taste buds. 

Each taste bud consists 
of a collection of spindle- 
shaped neurons, each cell 
tipped at its outer end 
with a hairlike projection. 
These cells send fibers in- 
ward to other cells, the fibers from which ultimately reach the 
brain. The sensory cells are surrounded by a number of pro- 
tecting cells which are arranged in layers about them. Thus 
h. bio — 29 




epithelial 
cell 

taste cetl- 
recejstor* 



...Cettboa; 



7 



A taste bud. Where is the sensation of taste found? 



438 MAN BECOMES THE CONQUEROR OF THE WORLD 



the organ in longitudinal section looks somewhat like an onion 
cut lengthwise. 

Four kinds of substances may be distinguished by the sense of 
taste. These are sweet, sour, bitter, and salt. Certain taste 
cells located near the back of the tongue are stimulated only by a 
bitter taste. Sweet substances are perceived by cells near the 
tip of the tongue, sour substances along the sides, and salt about 
equally all over the surface. Taste and smell are often confused 
and many things which we believe we taste are in reality perceived 
by the sense of smell. 

Smell. The sense of smell is located in the membrane lining 
the upper part of the nose. Here are found a large number of rod- 
shaped cells which are con- 



nected with the fore brain 
by means of the olfactory 
nerve. In order to perceive 
odors, it is necessary to have 
them, either as minute par- 
ticles of solid matter or as 




-olfcKttar^" cett 



Olfactory cells. 



Where is the sense of smell 
located ? 



gases, diffused in the air. 
If we wish to smell particularly well, we sniff so as to draw the air 
higher in the nasal chambers and nearer the olfactory cells. 

Hearing. The organ of hearing is the ear. The outer ear 
consists of a funnel-like organ composed largely of cartilage which 
is of use in collecting sound waves, and the auditory canal, which 
is closed at the inner end by a tightly stretched membrane, the 
tympanic membrane. The function of the tympanic membrane 
is to receive sound waves or vibrations in the air, which are trans- 
mitted, by means of a complicated apparatus found in the middle 
ear, to the inner ear. 

Middle ear. The middle ear is a cavity inclosed by the temporal 
bone, and separated from the outer ear by the tympanic membrane. 
A little tube called the Eustachian tube connects the inner ear 
with the mouth cavity. By allowing air to enter from the mouth 
the air pressure is equalized on the tympanic membrane. For 
this reason we open the mouth at the time of a heavy explosion 
and thus prevent the rupture of the delicate tympanic membrane. 



HEARING 



439 




-CochleoL 



..jltxstadhian tube 



Explain from the diagram, how we hear ? 



Placed directly against the tympanic membrane, and connecting 
it with another membrane which separates the middle from the 
inner ear, is a chain of three tiny bones, the smallest of the body. 
They are held in ,± 

place by very small g*?™** S^? e 22?* Served 
muscles which are 
delicately adjusted 
so as to tighten or 
relax the mem- 
branes guarding the 
middle and inner 
ear. 

The inner ear. 
The inner ear is one 
of the most com- 
plicated, as well as 
one of the most 
delicate, organs of the body. Deep within the temporal bone 
there are found two parts, one of which is called, collectively, the 
semicircular canals, the other the cochlea (kok'le-d). 

It has been discovered by experimenting with fish, in which 
the semicircular canal region forms the chief part of the ear, 
that this region has to do with the equilibrium or balancing of the 
body. 

That part of the ear which receives sound waves is known as the 
cochlea (Lat., snail shell) because of its shape. This complicated 
organ is lined with sensory cells provided with cilia, and its cavity 
is filled with a fluid. It is believed that somewhat as a stone 
thrown into water causes ripples to emanate from the spot where 
it strikes, so sound waves are transmitted by means of the fluid 
filling the cavity to the sensory cells of the cochlea and thence 
to the brain by means of the auditory nerve. 

The character of sound. When vibrations which are received 
by the ear follow one another at regular intervals, the sound is said 
to be musical. If the vibrations come irregularly, we call the 
sound a noise. If the vibrations come slowly, the pitch of the 
sound is low ; if they come rapidly, the pitch is high. The ear 



440 MAN BECOMES THE CONQUEROR OF THE WORLD 




is able to perceive as low as thirty vibrations per second and as 
high as almost thirty thousand. 

Seeing. The organ of vision, the eye, is almost spherical, and 
fits into a socket of bone, the orbit. A stalklike structure, the optic 
nerve, connects the eye with the brain. Free movement is made 
possible by means of six little muscles which are attached to 

the outer coat of the 
eyeball, and to the 
bony wall around 
the eye. 

The wall of the 
eyeball is made up 
of three coats. An 
outer tough white 
coat of connective 
tissue is called the 
sclerotic (skle-rot'ik) 
coat. In front, where 
the eye bulges out 
a little, this outer 
coat is replaced by a transparent tough layer called the cornea. 
A second coat, the choroid (ko'roid), is supplied with blood vessels 
and cells which contain pigments. The iris is part of this coat 
which we see through the cornea as the colored part of the eye. 
In the center of the iris is a small circular hole, the pupil. The 
iris is under the control of muscles, and may be adjusted to varying 
amounts of light, the hole becoming larger in dim light, and 
smaller in bright light. The inmost layer of the eye is called the 
retina (ret'i-nd). This is, perhaps, the most delicate layer in the 
entire body. Despite the fact that the retina is less than -^ of 
an inch in thickness, there are several layers of cells in its com- 
position. The optic nerve enters the eye from behind and spreads 
out over the surface of the retina. Its finest fibers are ultimately 
connected with numerous elongated cells, which are stimulated 
by light. The retina is dark purple in color, this color being due 
to a layer of cells next to the choroid coat. This accounts for the 
black appearance of the pupil of the eye, when we look through 



What happens to the eye when we pass from a brightly 
lighted room into a dark room ? 



SEEING 441 

it into the darkened space within the eyeball. The retina acts 
as the sensitized plate in the camera, for on it are received the 
impressions which are transformed and sent to the brain and result 
in sensations of sight. The eye, like the camera, has a lens. This 
lens is formed of transparent, elastic material. It is directly behind 
the iris and is attached to the choroid coat by means of delicate 
ligaments. In front of the lens is a small cavity filled with a 
watery fluid, the aqueous humor, while behind it is the main cavity 
of the eye, filled with a transparent, almost jelly-like, vitreous 
humor. The lens itself is elastic. This circumstance permits a 
change of form and, in consequence, a change of focus upon the 
retina of the lens. By means of this change in form, or accommoda- 
tion, we are able to see both near and distant objects. 

Practical Exercise 4. Make a diagram to show exactly what changes take 
place in the eye when you look from your book out of the window to focus on 
something coming down the far end of the street. 

Self-Testing Exercise 

There are areas on the skin that are sensitive to (1), 

(2), and (3). The organs of taste are the (4) 

(5). The kinds of substances distinguished by taste are 

(6), (7), (8), and (9). The 

sense of smell is located in the (10) lining the (11) 

part of the nose. The organ of hearing is the (12). It is 

composed of the (13), (14), and (15) 

(16). The (17) receives the sound waves which 

are transmitted to the (18) by the (19) (20). 

The eye is covered by three coats (21), (22), and 

(23). Impressions of seeing are made on the (24), 

which are carried to the (25) by the (26) 

(27). The (28) in form of the lens of eye is 

called (29). 

PROBLEM VI. WHAT BEHAVIORS ARE INSTINCTIVE? 

Demonstration 5. What actions of a newly hatched chick are in- 
stinctive ? 

Place a newly hatched chick on a small tray, with food and water. 
Place on the tray small, bright-colored, distasteful substances. Watch 
the chick and make careful record of all its actions. List as many as 
you can as instinctive. Are instinctive acts always useful? 



442 MAN BECOMES THE CONQUEROR OF THE WORLD 



Instinctive behavior. In many animals certain important 
behaviors in life are instinctive, that is, they are performed for 
the first time without being learned. A wasp lays its eggs in the 
body of a caterpillar, which it first paralyzes by stinging; the 
oriole weaves its nest ; the swallow builds its nest of mud ; 
the trapdoor spider makes its tunnel in the ground and furnishes 
it with a door — all these and thousands of other examples might 
be given. The complicated activities of the pronuba moth (see 
page 94) can be explained only by instinct, for the moth dies 

without ever seeing her 
offspring. 

Instincts can best be ex- 
plained, as workers with 
insects have shown, as a 
chain of inborn automatic 
responses or simple re- 
flexes. For example, an 
insect's making a nest, 
stinging the prey, and lay- 
ing eggs are a series of be- 
haviors, each one depend- 
ing upon the one before. 
If we interrupt the se- 
quence, as by removing 
most of the food supply 
from the nest, or by giving 
a fly paper soaked in meat 
juices, instead of decayed 
flesh, in which to lay its 
eggs, the life cycle is ended 
because the insect cannot 
modify its actions. As Professor Hodge says, a housefly is about 
as intelligent as a shot rolling down a board. Once the chain of 
behaviors is set in motion by some outside stimulus, it continues 
until the life cycle is completed by egg laying. 

Modification of instinctive behavior. Although the French 
naturalist, Fabre (fa'br'), found that a certain wasp which drags 




C. Clarke 



The squash bug fastens her brown shiny eggs with 
care beside the midrib of the underside of a large 
squash leaf which the larvas will feed upon as soon 
as they hatch. 



MODIFICATION OF INSTINCTIVE BEHAVIOR 443 

its grasshopper prey by one antenna would not touch its prey if 
both antennae were cut off, yet there are examples of instinctive 
behaviors being modified for the benefit of the animal. Some 
insect larvae, if they have consumed all of the plant on which they 
usually feed, will eat other kinds of leaves and thus save their 
lives. Fish and frogs can be taught to form new associations, for 
after many errors they will learn to avoid obstacles placed between 
them and their food. A dog can be taught to refrain from eating 
a lump of sugar placed on his nose until a word is spoken, because 
he has formed new connections which considerably change his 
natural behavior. Such modified responses, which are caused 
by new stimuli, are said to be conditioned. The new response 
made by the dog is conditioned by an association formed by the 
dog's master. 

Practical Exercise 5. Think of some of your pets, as a dog or a bird, and 
make a list of the instinctive acts performed by this animal. Have you ever 
tried to condition one of these instinctive responses? Why are instincts 
important in the lives of animals ? Give some examples of household pets that 
show how instincts may be modified. 

Self-Testing Exercise 

Instincts are usually explained as (1) (2) 

(3) . Instinctive acts are often (4) in lower 

animals. When simple (5) become (6), they are 

said to be (7). Such a reaction is usually caused by a new or 

different (8). If some animals are not able to (9) 

their (10), they die. 

PROBLEM VII. HOW ARE HABITS FORMED? 

Some of our earliest acts or behaviors are instinctive. Babies 
do not have to be taught to suck ; but as they grow older they 
modify this instinct. They learn to take food from a spoon and 
to wait for it. Later on they learn, by a series of trials, to stand 
erect and then to walk. There is a difference between the instinct 
of sucking and the habits which are learned through repetition 
when the child is compelled to take other food than its mother's 
milk. A habit might be called an acquired automatic activity. 



444 MAN BECOMES THE CONQUEROR OF THE WORLD 

Practical Exercise 6. For every good habit formed there is an opposite 
bad habit. From the list of good habits named below name the opposite bad 
habits. 



perseverance 


reliability 


neatness 


unselfishness 


obedience 


correct speech 


punctuality 


sociability 


orderliness 


conscientiousness 


courtesy 


modesty 


industriousness 


optimism 


observation 


poise 


habits of good posture 


cooperation 


inventiveness 


attentiveness 


regular toilet habits 


confidence 


classification 


enthusiasm 


honesty 


independence 


openmindedness 


self-reliance 


truthfulness 


diligence 


reasonableness 


frankness 


promptness 


accuracy 


alertness 


patience 


Which of the above-named habits do you 
form? 


have ? What habits should you 



Habit formation. One object of education is the training of 
the different areas in the cerebrum to do their work. When we 
first tried to write, we had to exert conscious effort in order to 
make the letters. Now the act of forming the letters is done 
without our thought. By training, the act has become a habit. 
The actual performance of the action is then taken up by the 
cerebellum, medulla, and spinal ganglia. Thus the thinking 
portion of the brain is relieved of this work. 

It is surprising how little real thinking we do during a day, for 
most of our acts are habitual. Habit takes care of our dressing, 
our bathing, our care of the body organs, our methods of eating. 
Even our movements in walking and our style of handwriting 
are matters of habit formation. We are bundles of habits, be they 
good ones or bad ones. 

Different kinds of habits. Habits are of many kinds. They 
may concern health and well-being, as proper tooth brushing, eat- 
ing at regular times, maintaining a correct posture, and hundreds 
of simple things we do automatically. Some concern our dress and 
our actions in society. We walk, ride, dance, skate, or drive a car 
without consciously thinking about what we are doing. Our habits 
of disposition have become a very important part of our lives. We 
may frequently be sad or be happy, sing or cry, or be kind, or be 
cross. We may form our habits of thought, too : concentration 
or scatter-brain methods, ability to think through our problems, 
or inability to do any real thinking — it all depends upon ourselves. 
Man has conquered many factors in his environment through 



FORMING RIGHT HABITS 445 

training his body to do certain things effectively. The most 
important thing is the control of his nervous system, because it is 
through the effective use of it that he gets things done. If you 
will be conqueror in your sphere of life, learn how to control your 
own thoughts and deeds. In this way you will be prepared to 
conquer in the bigger field of activity which you will enter later. 

Habits must be formed early. We have often heard the saying, 
" You can't teach an old dog new tricks." This is all too true 
of habit forming. We exercise our muscles and they grow larger. 
Not so with our brain cells. We probably all have the same 
number of neurons, but there is an unlimited number of possible 
connections between them, which may result in a great many 
habitual activities. Every time a new act is performed a new 
connection, synape, is made between two neurons. While the 
nervous system is young the cells are plastic, and pathways are 
easily established between cells. These pathways, like a rut in 
soft mud, become deeper and deeper with use. Habits are, there- 
fore, readily formed at this time. " Practice makes perfect " is a 
truism, but it illustrates how a habit is formed. Fortunate are 
the boys and girls of the age who read this book, for they are able 
to form good habits easily. But a man or woman of middle age 
has formed habits, and to change them and make new ones is very 
difficult. The nervous system is no longer plastic. 

Practical Exercise 7. What are the best ways of forming good habits? 
Write a short composition on this for your workbook. 

What is the advantage of forming good habits in life ? Does habit-forming 
relieve part of the nervous system from work? Explain fully. Explain the 
increased effectiveness and power acquired through good habits. 

Importance of forming right habits. Among the habits which 
should be acquired early in life are those of studying properly, of 
concentrating the mind, of learning self-control, and, above all, of 
being content. Get the most out of the world about you. Re- 
member that the immediate effect of the study of some subjects 
in school may not be great, but the cultivation of correct methods 
of thinking may be of the greatest importance later in life. The 
men and women who have learned how to concentrate on a prob- 
lem, how to weigh all evidences with unbiased minds, and then to 



446 MAN BECOMES THE CONQUEROR OF THE WORLD 

decide on what they believe to be right, are the efficient and happy 
ones of their generation. 

" The hell to be endured hereafter, of which theology tells, is no 
worse than the hell we make for ourselves in this world by habitually 
fashioning our characters in the wrong way. Could the young but 
realize how soon they will become mere walking bundles of habits, 
they would give more heed to their conduct while in the plastic state. 
We are spinning our own fates, good or evil, and never to be undone. 
Every smallest stroke of virtue or of vice leaves its never-so-little scar. 
The drunken Rip Van Winkle, in Jefferson's play, excuses himself 
for every fresh dereliction by saying, ' I won't count this time ! ' 
Well! he may not count it, and a kind Heaven may not count it; 
but it is being counted none the less. Down among his nerve cells 
and fibers the molecules are counting it, registering and storing it up 
to be used against him when the next temptation comes. Nothing we 
ever do is, in strict scientific literalness, wiped out. Of course this 
has its good side as well as its bad one. As we become permanent 
drunkards by so many separate drinks, so we become saints in the 
moral, and authorities in the practical and scientific spheres, by so 
many separate acts and hours of work. Let no youth have any 
anxiety about the upshot of his education, whatever the line of it may 
be. If he keep faithfully busy each hour of the working day, he may 
safely leave the final result to itself. He can with perfect certainty 
count on waking up some fine morning, to find himself one of the com- 
petent ones of his generation, in whatever pursuit he may have singled 
out." — William James, Psychology. (Permission of Henry Holt & Co.) 

Some rules for forming good habits. Professor Home gives 
several rules for making good or breaking bad habits. They are : 
First, act on every opportunity. Think of the good habits you would 
like to form and then form them. Second, make a strong start. 
No half-hearted effort ever was successful in forming a habit. 
Third, allow no exception. You cannot establish the new pathway 
in the nervous system, if you, like Rip Van Winkle, " don't count 
this one." Fourth, for the bad habit establish a good one. Most of 
us know our own faults. Some of us have far too many. Per- 
haps it is only a little thing such as forgetting some of the numerous 
conventionalities that make up table manners ; it may be some- 
thing far more important, an uncontrolled emotion or feeling. 



GOOD HABITS 447 

Anyway, there is some opposite helpful habit you can substitute 
in its place. For example, instead of saying sometimes, " That 
noise drives me wild," say nothing, but think to yourself, " there's 
no noise that I can't stand when necessary." Fifth, use effort of 
will. Habits which are rooted when young in moral and religious 
training are those which in later life will do more than any others 
to steer us straight on the course we would take through life. 

Practical Exercise 8. Explain how you would break some specific bad 
habit by using the rules quoted above: 

Make a list of habits of mind that you would like to acquire. How would 
you go to work to do this? 

Self-Testing Exercise 

A habit is an acquired (1) act. Learning to (2) is 

such an act. Habits are most easily formed when we are (3). 

" Practice makes perfect " is a good rule in (4) (5). 

In forming a habit : Act on every (6) ; make a strong 

(7) ; allow no (8) ; replace (9) habits with 

(10) habits ; use your (11) of (12). 

PROBLEM vTIL WHAT ARE SOME GOOD HEALTH HABITS? 

Health habits for the nervous system. The nerve cells, like 
all other cells in the body, are continually wasting away and being 
rebuilt. Oxidation of food material increases when we do mental 
work. The cells of the brain, like muscle cells, are not only 
capable of fatigue, but they show this in changes of form and of 
contents. Food brought to them in the blood, plenty of fresh air, 
and rest at proper times, are essential in keeping the nervous system 
in condition. One of the best methods of resting the brain cells 
is a change of occupation. Tennis, golf, baseball, and other 
outdoor sports combine muscular exercise with brain activity of a 
different sort from that of business or school work. 

Necessity of sleep. But change of occupation will not rest 
exhausted neurons. For this, sleep is necessary. Especially is 
sleep an important factor in the health of the nervous system of 
growing children. A child needs ten hours of sleep, an adult, 
eight hours. When a person is sleeping, his brain cells have oppor- 
tunity to rest and to store food and energy for their working period. 



448 MAN BECOMES THE CONQUEROR OF THE WORLD 



.large 
^ran tele 





rested, 
oell 



S^ 



tired 
eel] 



Sleep is one way in which all the cells in the body, and par- 
ticularly those of the nervous system, get their rest. The nervous 

system, by far the most delicate 
and hardest-worked set of tissues 
in the body, needs rest more than 
do other tissues, for much of its 
work of directing the body ends 
only with sleep or unconscious- 
ness. The afternoon nap, snatched 
by the brain worker, gives him re- 
newed energy for his evening's 
work. It is not hard application 
to a task that wearies the brain ; it 
is continuous work without rest. 

Health habits for the sense or- 
gans. Overstimulation of any of 
the sense organs is a bad thing. 
The ear may be overstimulated 
by loud noises; the eye by too 
bright light; the olfactory cells 
by too heavy odors, the taste cells by too highly seasoned food. 
The most frequent habits of abuse of the eyes are using them for 
reading in a dull or flickering light or in too bright a light which 
makes a glare on the page. We should avoid looking directly into 
the source of any light. 

The eyes are also subject to infection and injury from dust, cin- 
ders, flying bits of metal, etc. Certain trades in the past have 
taken a high toll of eye injuries, although now workers are pro- 
tected by proper goggles. In case of soreness or irritation place a 
drop of newly prepared weak solution of argyrol in each eye. This 
may prevent serious eye trouble. 

Many eyes are imperfect because the curvature of the lens is not 
normal. Such defects are a cause of headaches, and should be 
remedied by having an oculist prescribe corrective glasses. 

Practical Exercise 9. Make two lists — one of habits practiced by you 
that are detrimental to health and the other one of habits that promote good 
health. What can you do to improve your health? Show what habits would 
result in the protection of your eyes. 



The effect of fatigue on a nerve cell. 
What has happened to the dark granules 
characteristic of a normal cell ? 



THE RELATION OF ALCOHOL TO EFFICIENCY 449 

Self-Testing Exercise 

(1), (2), and (3) (4) are necessary 

to keep brain cells healthy. Change of occupation is good for exhausted 

neurons but (5) is better. The most frequent abuses to the eyes 

are reading in a (6) (7) (8) or in a (9) . 

PROBLEM IX. WHAT ARE SOME EFFECTS OF THE DRINK 

HABIT? 

The drink habit. Although prohibition has made it harder for 
all people to obtain liquors, many still drink and some seemingly 
cannot help it. Let us see why. 

The first effect of drinking alcoholic liquors is that of exhilaration. 
After the feeling of exhilaration is gone, for this is a temporary 
state, the drinker feels depressed and less able to work than before 
he took the drink. To overcome this feeling, he takes another 
drink. The result is that before long he finds a habit formed from 
which he cannot easily change. 

The economic effect of alcoholic poisoning. In the struggle 
for existence, it is evident that the man whose intellect is the quick- 
est and keenest, whose judgment is most sound, is the man who 
is most likely to succeed. The deadening effect of alcohol upon the 
nerve centers must place the drinker at a disadvantage. 

Dr. Parkes experimented with two gangs of men, selected to be 
as nearly similar as possible, in mowing. He found that with one 
gang abstaining from alcoholic drinks and the other not, the 
abstaining gang could accomplish more. On taking away the 
alcohol from the one gang and giving it to the other, the same 
results were obtained. Similar results were obtained by Professor 
Aschaffenburg of Heidelberg University, who found, experimentally, 
that men " were able to do 15 per cent less work after taking 
alcohol." Many other experiments along the same lines have 
been made. In typewriting, in typesetting, in bricklaying, and 
in the highest type of mental work, the result is the same. The 
quality and quantity of work done by men on days when they 
take alcohol is less than on days when they take no alcohol. 

The relation of alcohol to efficiency. We have already seen 
that neither is work done as well nor is as much accomplished by 



450 MAN BECOMES THE CONQUEROR OF THE WORLD 

drinkers as by non-drinkers. Some relation of alcohol to efficiency- 
is shown by the chart below, which was made prior to prohibition. 
During the week the curve of working efficiency is highest on 
Friday and lowest on Monday. The number of accidents were 




This chart was made prior to prohibition. Can you explain why the above facts were true ? 



also least on Friday and greatest on Monday. Lastly the assaults 
were fewest in number on Friday and greatest on Sunday and 
Monday. 

Since the prohibition law went into effect, welfare organiza- 
tions have reported a great decrease in cases of destitution and 
dependence caused by drink. Workmen today are saving their 
wages or investing in radio sets or in automobiles instead of 
drink. This is one of the greatest arguments in favor of pro- 
hibition. 

The relation of alcohol to crime. A study, made just before 
the eighteenth amendment was passed, of more than 2500 habitual 
users of alcohol, showed that over 66 per cent had committed crime. 
Of 23,581 criminals questioned, 20,070 said that alcohol had led 
them to commit crime. 

The relation of alcohol to pauperism. Studies of certain families 
which have long been a heavy burden on the state show that 
alcohol is at least partly responsible for their condition. Alcohol 
weakens efficiency and moral courage, and thus leads to begging, 
pauperism, petty stealing or worse, and ultimately to life in some 



TEST ON FUNDAMENTAL CONCEPTS 451 

public institution. In Massachusetts, of 3230 inmates of such 
institutions, 66 per cent were alcoholics. 

Practical Exercise 10. Sum up the reasons why alcohol harms a person 
through its effects on the nervous system. 

Self-Testing Exercise 

Alcohol is a (1). There seems to be a direct correlation 

between drinking and (2), and between drinking and 

(3). Some experiments show that drinkers are (4) 

(5) than non-drinkers. The (6) of (7) is 

hard to overcome. Alcohol has harmful effects upon the (8) 

system. 

Review Summary 

Check your knowledge of the unit by: (1) rechecking on the survey ques- 
tions ; (2) performing the assigned exercises ; (3) checking with your teacher 
the scores of the various tests and doing over all missed parts ; (4) making an 
outline of the unit for your workbook. 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you be- 
lieve are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 2\. 

I. Sense organs (1) are never located at the surface of the body; 

(2) usually consist of cells which are capable of receiving stimuli; 

(3) in lower animals are usually located in hairs or other structures 
at the outside of the body ; (4) put animals in touch with their sur- 
roundings ; (5) are usually more numerous at the anterior end of an 
animal. 

II. A reflex (6) is a structure formed on the outside of animals; 

(7) is seen in plants when the leaves close up in response to heat or light ; 

(8) is the result of a stimulus and results in movement ; (9) is seen 
when we involuntarily withdraw our finger from a hot object; (10) is 
the result of a nerve impulse traveling to a nerve center, where it is 
translated into movement by means of an outgoing nerve impulse. 

III. Stimuli (11) travel by means of nerves; (12) are received 
through sense organs; (13) often are felt as pain, pressure, heat; 
(14) are of no value to man; (15) are the means by which we are 
aware of our surroundings. 



452 MAN BECOMES THE CONQUEROR OF THE WORLD 

IV. We see (16) by means of the retina which receives the light 
images ; (17) in the brain and not in the eye ; (18) because the retina 
transforms the stimulus caused by the light waves and transmits them 
by the optic nerve to the brain ; (19) because our eye is like a camera 
— the eye becoming deeper or more shallow as we focus ; (20) when 
through a change of shape the lens is focused on an object. 

V. The sense organs of man (21) are the nose, tongue, eyes, and 
skin ; (22) are all external ; (23) are connected by nerves with the central 
nervous system ; (24) are made up of sensory cells ; (25) are not deli- 
cate enough to need protection, and so do not have any. 

VI. Instincts (26) are actions that are performed without having 
first been learned ; (27) are behaviors which are useful because they 
help preserve the race; (28) are acts that are carefully thought out 
before they are performed; (29) may be modified or conditioned 
through teaching ; (30) serve to avoid dangers. 

VII. Habits (31) may be either harmful or useful ; (32) are learned 
activities ; (33) may be mental or physical ; (34) make up a large part 
of our life activities ; (35) cannot easily be learned by young people. 

VIII. The following are good rules for forming desirable habits : 
(36) never use will power; (37) allow no exceptions to occur; 
(38) never make a strong start; (39) have a real desire to build the 
habit ; (40) act on every opportunity to make the desired reaction. 



Achievement Test 

1. How can you demonstrate what a tropism is and how it causes 
a living thing to react ? 

2. What are the different stimuli that affect the lives of plants and 
animals ? 

3. What is meant by the method of trial and error? 

4. How can you demonstrate a reflex act? 

5. Locate the parts of your nervous system, and tell the uses of 
each part. 

6. How do we taste, touch, and feel hot or cold objects? 

7. How do we hear? 

8. How do we see? How can we compare the human eye to a 
camera ? 

9. How would you define instinct? 

10. Wliat is meant by a " conditioned " reflex? 



USEFUL REFERENCES 



453 



11. How can you take the proper steps in forming a good habit or 
breaking a bad one? 

12. Why cannot one " teach an old dog new tricks "? 



Practical Problems 

1. Fill out the following table with reference to the sense organs in the 
human body. 



Organs 


Location 


What They Do 


How They Do It 











2. Show exactly what happens in your nervous system when you touch 
a hot object in the dark. 

3. How would you go to work to eradicate a bad habit? 

4. Show that some act of your daily life isa" conditioned reflex." 

Useful References 

Dorsey, Why We Behave Like Human Beings. Chap. vi. (Harper & 

Bros. 1925.) 
Fabre, The Wonders of Instinct. (The Century Co. 1918.) 
Home, Psychological Principles of Education. (The Macmillan Co.) 
Hunter, Laboratory Problems in Civic Biology. Pp. 161-168, inc. (American 

Book Company.) 
James, Talk to Teachers on Psychology. (Henry Holt & Co. 1914.) 
Jewett, Control of Body and Mind. (Ginn & Co.) 
Loeb, Forced Movements, Tropisms and Animal Conduct. Chap, xviii. 

(J. B. Lippincott and Co. 1918.) 
Watson, Psychology from the Standpoint of a Behaviorist. (J. B. Lippincott 

and Co. 1924.) 



H. BIO — SO 



SURVEY QUESTIONS 

Why do people have a longer expectancy of life today than 30 years ago ? 
Why do some people take a catching disease and others who are exposed 
do not? Why are people vaccinated against smallpox? How are children 
made immune against diphtheria ? What are the purposes of a Medical 
Center, as the Cornell Medical Center, New York, shown here ? 



Eiving Galloway 



454 



PART V. MAN'S INTERRELATIONSHIP WITH 
OTHER LIVING THINGS 

UNIT XV 

HOW DOES MAN CONTROL HIS ENVIRONMENT 
FOR HEALTH? 

Preview. The body has been likened to an engine, in that each 
requires fuel and oxygen to work, produces wastes, and must have 
frequent rest in order to do efficient work. Both the machine and 
body may eventually wear out. But we do not speak of a sick 
machine, although we do speak of a sick person. What, then, is 
health? It is evidently a state in which the human machine 
runs efficiently. It is a state of well-being, or being well. A 
person may so abuse his body through lack of sleep, or exercise, 
or proper food that soon his body will not function properly. He 
may poison his body with alcohol or nicotine, and injure some of 
his internal organs so that he never recovers his former efficiency. 
He may meet with an accident and be crippled, or he may be 
attacked by some microscopic foes, bacteria, and suffer from 
infectious diseases. Diseases caused by these microorganisms 
cause more than half the common ailments of young people. 

We have already learned something concerning the relation 
of bacteria and other colorless plants to disease. It is the purpose 
of this unit to show how some animals play a part in the cause and 
spread of disease. It is obvious that the relation is twofold. 
Animals may be parasites in man, causing certain diseases, or 
they may, acting as hosts, carry a parasite for part of their life 
histories. The malarial parasite and the hookworm are examples 
of the first type ; the mosquito, which carries the malarial parasite, 

455 



456 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

and the flea, which transmits bubonic plague bacilli, are examples 
of the second type. 

It is comparatively recently that we have discovered some of the 
very definite ways in which these parasites do us harm. I am not 
an old man. but I can well remember how my father used to keep 
me in at dusk as he pointed to the mist rising from the lowlands 
next the river and said. " See the malaria rising there. 7 ' We did 
not know, little more than 30 years ago, that a certain kind of 
mosquito carried the organism that causes malaria and that the 
only connection between the mist and malaria was that those 
low-lying marshlands were alive with the mosquitoes which carry 
the disease organisms within their bodies. 

In the control of diseases, prevention is far more important than 
attempts to cure. Experimentation and experience have taught 
us that health is closely associated with conditions in man's 
environment. TVe have learned to isolate the sick from the well, 
so that diseases may not be communicated. Many diseases have 
been partially or entirely controlled through scientific investiga- 
tion and health education. Immunity or protection against dis- 
ease may be both natural and acquired. The former is the immu- 
nity that one has at birth and stays with one throughout his life. 
The latter is acquired through the use of antitoxins, weakened 
living germs, dead germs, or extracts containing poisons made by 
germs, introduced into the body. 

Doubtless it seemed irksome and needless to some of you that 
during an attack of measles the doctor insisted not only that you 
should be isolated from the rest of the young people in the family 
but also that you be kept in a darkened room for several days. Now, 
measles is not an eye disease and you may have wondered why 
he did this. If you had been older and wiser, you would have 
realized that certain parasitic diseases are more feared for the 
harm they may do the individual in later life than what they 
do at the time. Doctors could tell you of many cases where 
measles or scarlet fever have left a trail of weakened body 
organs which have made people semi-invalids and sent some 
to early graves. It pays to care for oneself at the time of an 
illness. 



THE GROWTH OF BACTERIA 457 

We also hear a good deal nowadays about the increase in the 
length of the life span. In every country except India in which 
vital statistics are available the expectation of life is steadily 
lengthening. In England, for example, in the decade between 1870- 
1880 the average expectancy of life for a child at birth was 42.98 
years. In 1922 it was 56.95 years. In Massachusetts, where 
vital statistics have been kept for a longer period than some other 
states, in 1855 the expectancy of life was 39.77 years, in 1920 it 
was 55.25. In the United States (registration area), in 1901, the 
expectancy of life was 49.24 years, in 1926 it was 57.74 years, 
and at the present time it is over 58 years. Why is this so? 
Principally because we are gaining mastery over the diseases 
caused by bacteria and especially diseases of young children. 
Dr. Vincent of the Rockefeller Foundation said recently that 80 
per cent of the illnesses of man could be avoided if people were 
willing to obey health laws and live as well as they know how. 
Then, too, we are learning that health is closely associated with 
conditions in man's environment and that it pays from every view- 
point to have good sanitation and housing. We are learning to 
quarantine the sick, so that diseases may not be so easily com- 
municated as in the past. And we have built many and vast 
" temples of healing " — hospitals and sanitariums, where the sick 
are brought back to health. 



PROBLEM I. HOW MAY WE CONTROL THE GROWTH OF 

BACTERIA? 

Demonstration 1. To show the effect of temperature on the growth 
of bacteria. 

Number four tubes containing bouillon. Place number one in 
the ice box, number two in a dark box at a moderate temperature, 
number three in a box at a hot temperature (120° F. or over), and 
boil number four for 15 minutes and then place with number two. 

Note in which tube the greatest amount of growth takes place. 
Note the odor as well as the color of bouillon. Note in which tube the 
least growth takes place. 

Describe the effect of intense heat on bacteria? Would the sand 
of a desert contain many bacteria? The ice of the polar regions? 
From this experiment we derive the very important method of fighting 
bacteria by means of sterilization. Give a definition of sterilization. 



458 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



valve 



gauge, 




Why anl when is a pressure cooker used? 



Sterilization. Bacteria grow very slowly, if at all, in the tem- 
perature of an ice box, very rapidly from 70° to 98°, and much less 
rapidly (or are killed) at a higher temperature. Those bacteria 
which form spores resist a great deal of heat and may even be 

boiled for some time without 
injury. The practical lessons 
drawn from these facts are 
many. We boil our drinking 
water if we are uncertain of its 
purity ; we cook foods that we 
believe might harbor bacteria, 
and thus keep them from spoil- 
ing. The industry of canning 
is built upon this method of 
sterilization. 

Canning. Canning is simply 
a method by which first the 
bacteria in a substance are killed 
by heating and then the substance is put into vessels and covered 
so that no more bacteria can gain entrance. The use of canned 
goods has completely changed the life of the sailor and the soldier, 
who in former times used to suffer from various diseases caused 
by lack of a proper balance of food. 

Practical Exercise 1. What is the " cold pack " method of canning ? What 
scientific principles are used in canning ? 

Cold storage. Man has learned to use cold to keep bacteria 
from growing in foods. The refrigerator at home and cold storage 
on a larger scale enable us to keep foods for a more or less long 
period. If food is frozen, as in cold storage, it might keep without 
growth of bacteria for years. But frozen foods after thawing are 
particularly susceptible to the bacteria of decay. For that reason 
products taken from cold storage must be used as soon as possible. 

Demonstration 2. To determine the effect of pasteurization on the 
keeping quality of milk. 

Place half of the milk in a sterilized jar, cover, and leave in a warm 
place for 24 to 48 hours. 

Place the remainder of the milk in another jar, cover, and put it 
in the double boiler or pasteurizing apparatus. Keep the hot water 



PASTEURIZATION 459 

surrounding the jar from 160° to 180° F. for about 30 minutes. This 
is known as pasteurization. Afterwards treat exactly as you did the 
first jar of milk. 

What is the odor of milk in each jar after 24 and 48 hours? What 
is the taste of the milk in each jar after 24 and 48 hours? 

What are found in milk that cause it to sour? How do you know? 
What is the use of pasteurization ? 

Pasteurization. Milk is one of the most important food sup- 
plies of mankind. It is also one of the most difficult things to get 
in good condition. This is due in part to the fact that milk is 
often produced at long distances from the place where it is used 
and must be brought first from farms to the railroads, then shipped 
by train, taken to the milk supply depot, bottled, and again taken 
by delivery wagons to the consumers. During each successive 
handling and exposure to the air the milk receives more bacteria. 
When we remember that much of the milk used in San Francisco, 
St. Louis, Chicago, New York, and other large cities is from twelve 
to thirty-six hours old before it reaches the consumer, and when 
we realize that bacteria grow very rapidly in milk, we see the need of 
finding some way to protect the supply so as to make it safe, par- 
ticularly for babies and young children. This is done by pasteuri- 
zation, a method named after the French bacteriologist, Louis 
Pasteur. 

Preservatives. A few substances check the development of 
bacteria and in this way preserve the food. Preservatives are of 
two kinds, those harmless to man and those that are poisonous. 
Of the former, salt and sugar are examples ; of the latter, formalde- 
hyde and possibly benzoic acid. 

Sugar. We have noted the use of sugar in canning. Small 
amounts of sugar are readily attacked by yeasts, molds, and 
bacteria, but a 40 or 50 per cent solution will effectually prevent 
such growths. Preserves are fruits boiled in about their own 
weight of sugar. Condensed milk is preserved partly by the sugar 
a,dded to it ; so are candied fruits. 

Salt. Salt has been used for centuries to keep foods. Meats 
are smoked, dried, and salted ; some are put down in strong salt 
solutions. Fish, especially cod and herring, are dried and salted. 
The keeping of butter is due to the salt mixed with it. Vinegar 



460 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

is another preservative. It, like salt, changes the flavor of mate- 
rials kept in it and so cannot come into wide use. Spices are also 
all used as preservatives. 

Harmful preservatives. Certain chemicals and drugs, used as 
preservatives, seem to be on the border line of harmfulness. Such 
are benzoic acid, borax, and boracic acid. These chemicals may 
be harmless in small quantities, but unfortunately in canned 
goods we do not always know the amount used ; also, as a rule, 
food that needs such a preservative is of bad quality in the first 
place. The Pure Food Law makes it illegal to use any of these 
preservatives in food (excepting very small amounts of benzoic 
acid). Food which contains this preservative must be so labeled 
and should not be given to children or people with weak digestion. 
Unfortunately, people do not always read the labels, and thus the 
Pure Food Law is ineffective in its working. 

Demonstration 3. To determine the most effective disinfectants. 

Inoculate test tubes containing bouillon with germs from a Petri dish 
culture. Number and label the tubes. Expose all tubes, unplugged, 
to air. 

To tube one add 1 drop formalin, 
two add 5 drops formalin, 
three add 1 drop lysol. 
four add 3 drops lysol. 
five add 1 drop iodine, 
six add 5 drops iodine, 
seven add 4 drops carbolic acid, 
eight add 10 drops carbolic acid, 
nine add 1 drop bichloride mercury solution, 
ten add 5 drops bichloride mercury solution, 
eleven add 5 drops mercurochrome. 
twelve add 15 drops mercurochrome. 

Tabulate daily, for a week or more, the results for the contents of each 
tube on a table. 

Which of the above is the best disinfectant? Why do you answer 
as you do? (Remember that according to definition an antiseptic may 
retard the growth of bacteria but will not of necessity kill them; a 
germicide destroys all bacteria if used properly; while a disinfectant 
is a solution used to kill disease germs, usually in the excreta of sick 
people.) 

Practical Exercise 2. Using the data from the preceding demonstration, 
classify the materials used, as antiseptics, germicides, or disinfectants. Give 
a reason for each. 



BACTERIAL DISEASES 461 

Disinfection. Frequently it becomes necessary to destroy 
bacteria with chemicals. This process is called disinfection. 
Although sunlight, dry heat, steam, and electricity kill germs, we 
commonly apply the term " disinfectant " to such substances as 
iodine, mercurochrome, potassium permanganate, chloride of lime, 
carbolic acid, formaldehyde, lysol, and bichloride of mercury. Of 
these, the last named is one of the most powerful as well as the 
most dangerous disinfectant to use. As it attacks metal, it should 
not be used in a metal pail or dish. It is commonly put up in 
tablets which are mixed to form a 1 to 1000 solution. Care 
must be taken of both the tablets and the solution to avoid a 
possible accidental poisoning. 

Formaldehyde in solution, called formalin, is used as a disin- 
fectant. When vaporized, it sets free an intensely pungent gas. 
Carbolic acid is an excellent disinfectant although it will not 
kill spores of bacteria. If used in a solution of about 1 part to 25 
of water, it will not burn the skin. It is of particular value in 
disinfecting skin wounds. Lysol is another excellent disinfectant, 
because it can be used with soap. Iodine is often used as a skin 
disinfectant and in open wounds. One of the newest germicides 
is mercurochrome. It is particularly valuable for wounds and 
skin bruises in which bacteria might thrive. 

Self-Testing Exercise 

(1) kills bacteria. Canning makes use of the principle 

of (2) . Pasteurization of milk is performed best by heating 

for (3) minutes to a temperature of from (4) to 

(5) F. Harmless preservatives are (6), (7), 

(8), and (9). Antiseptics are used to (10) 

the (11) of (12). Disinfectants are used to 

(13) (14). A germicide (15) all (16). 

PROBLEM II. HOW DO BACTERIA CAUSE DISEASE? 

Bacterial diseases. Bacteria cause many diseases in man. They 
accomplish this by becoming parasites in the human body. Mil- 
lions upon millions of bacteria exist in the human body at all times 
— in the mouth, on the teeth, and especially in the lower part of 




462 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

the food tube. Some in the food tube are believed to be useful, 
some harmless, and some harmful; others in the mouth cause 
decay of the teeth, while a few species may cause disease. Such 

disease-causing bacteria are 
called pathogenic. 

It is known that bac- 
teria, like other living 
things, take in food, form 
organic wastes within their 
own bodies, and give off 
some of them. These 
wastes, called toxins, are 
poisonous to the host on 
which the bacteria live, 
and cause the symptoms 
of certain diseases. Each 
species of bacteria forms 
Roy M.Aiien its own specific toxin, and 

A microphotograph of a Petri dish containing a pure this has a Specific action 
culture of bacteria that cause cholera. ^ 

on the body, causing the 
symptoms of a specific disease. As bacteria can multiply rapidly 
in the body, they may become very numerous before the body 
defenses gain control of the situation. When the bacteria die, as 
they may in great numbers during the progress of the disease, 
their bodies break down, and the released protoplasmic constit- 
uents, particularly the proteins, separate from each other and 
split into smaller and smaller molecular groups, as do the proteins 
when changed to amino acids during digestion. These split pro- 
teins, as they are called, are extremely poisonous to the body 
tissues and act as toxins in the body, causing many of the charac- 
teristic symptoms of disease. 

Some bacteria break down the body tissues, besides producing 
toxins. They may destroy the intestinal lining, or destroy the 
blood corpuscles, or break down tissues in wounds, thus causing 
specific symptoms of disease. 

It was estimated not many years ago that bacterial diseases 
caused annually almost 50 per cent of the deaths of the human 



HOW WE GET DISEASES 463 

race. A very large proportion of these diseases might have been 
prevented if people were educated sufficiently to take the proper 
precautions to prevent the spreading of bacteria. Such precau- 
tions might have saved the lives of some 3,000,000 people yearly 
in Europe and America. Tuberculosis, typhoid fever, bubonic 
plague, diphtheria, pneumonia, blood poisoning, and a score of 
other diseases ought not to exist. But within the last decade, 
due to the sacrifices and discoveries of men in medical science, the 
control of a number of bacterial diseases has been made possible. 
It is estimated, for example, that with the cooperation of the people, 
diphtheria might have been stamped out in New York state by the 
end of the year 1930. That this has not happened is due certainly 
to the number of uninformed people who will not or do not know 
how to cooperate with the medical authorities. A large amount 
of the present misery of this world might be prevented, and this 
earth made cleaner, better, and safer, by the cooperation of young 
people in carrying out and enforcing health regulations. 

Practical Exercise 3. Make a table to show all the ways in which bacteria 
may cause disease and give an example under each heading. 

Self-Testing Exercise 

Bacteria cause almost (1) (2) (3) of the 

(4) of the human race. Many of these might have been 

(5) if people would (6) with the medical authori- 
ties. Bacteria cause disease either by forming (7), releasing 

(8), or by (9) on the (10), thus breaking 

them down. 



PROBLEM III. HOW DO WE GET BACTERIAL DISEASES? 

How we get diseases. Bacteria causing infectious diseases enter 
the body either by the mouth, nose, or other body openings, or 
through a break in the skin. They may be carried by means of 
air, food, or water, but are more often transmitted directly from 
the person who has the disease to a well person. They may be 
acquired through personal contact, as kissing; in a spray of 
tiny droplets which are expelled into the air as a person talks; 



464 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

by handling or using articles, such as towels, handkerchiefs, cups, 
or dishes used by sick persons ; or by drinking or eating foods 
which have received some of the germs. 

Practical Exercise 4. Make a table to show all the ways in which bacteria 
gain entrance to the body and name a disease which gets into the body under 
each heading. 

Project. To make a curve showing decrease of tuberculosis in your 
own state. (Use State Board of Health or Public Health Service 
Reports for this and following projects.) 

Tuberculosis. One of the diseases responsible for the greatest 
number of deaths, perhaps one tenth of the total on the earth, is 
tuberculosis. Fisher estimates that tuberculosis has cost this 
country between $500,000,000 and $1,000,000,000 a year, by its 
toll of death, loss of work, maintenance of hospitals, sanitariums, 
etc. But this disease is slowly but surely being overcome. It is 
believed that within perhaps fifty years, with the aid of good laws 



BOO 


1850 I860 1870 1880 1890 1900 19IO \9SO 1930 V940 




4O0 
5oo 
2oo 

too 

O 




















































































































* % *.. 


? 











The number of death per 100,000 from tuberculosis has been steadily decreasing each year. 
If this rate continues there will be very few deaths in 1940 from this disease. 



and sanitary living, it might become almost extinct. In 1900, the 
death rate in the United States was 195.2 for each 100,000 inhab- 
itants, in 1926 the death rate in the same area was only 84.5 per 
100,000. In other words, according to Dr. Louis J. Dublin, there 



TUBERCULOSIS 465 

are about 130,000 fewer persons dying from tuberculosis each year 
in the United States than would have died if the tuberculosis 
death rate for 1900 still held for this area. 

Tuberculosis is caused by the growth of bacteria, called the 
tubercle bacilli, within the lungs or other tissues of the human body. 
In the lungs they form little tubercles full of germs, which close up 
the delicate air passages, while in other tissues they may cause 
hip- joint disease, scrofula, lupus, and other diseases, depending 
on the part of the body they attack. Tuberculosis may be con- 
tracted by taking bacteria from people who have the disease, or 
by drinking milk from tubercular cows, for the germ that affects 
cattle causes some of the tuberculosis in children. Dr. William 
H. Park, a noted authority on bovine (cow) tuberculosis, states 
that in a large number of cases investigated by him 57 per cent of 
abdominal tuberculosis in very young children and 47 per cent of 
such tuberculosis in children under five years of age were of the 
bovine type. Fortunately, the germs of bovine tuberculosis can 
be killed by pasteurization of milk of doubtful purity. 

Practical Exercise 6. Name some ways in which tuberculosis might be 
passed from one person to another. 

Most of us probably take into our lungs at one time or another 
bacteria causing tuberculosis. Yet the bacteria seem able to gain 
a foothold only under certain conditions. It is only when the 
tissues are in a wornout condition, when we are " run down," as 
we say, that the parasite may obtain a foothold in the lungs or 
other organs. The disease may be arrested, and a permanent 
cure is often brought about, by a life in the open air, the patient 
living and sleeping out of doors, taking plenty of nourishing food, 
and very little exercise. The object of this kind of life is to build 
up the body resistance, so that the germs are rendered incapable of 
doing harm. 

Tuberculosis is a serious disease to combat, because of the con- 
ditions which help to cause it. Contrary to common belief, it is 
not inherited ; but unfortunately in families where there are tuber- 
cular persons, it is difficult to prevent giving the germs to people 
living with them, especially if they live in small crowded homes 



466 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

with little ventilation. Children of tubercular parents are often 
handicapped by a weak constitution and are therefore very sus- 
ceptible to the disease. 

Practical Exercise 6. Tuberculosis is said to be a social disease. Explain 
this statement. 

Project. To determine the seasonal variation in the number of cases 
of diphtheria in your state. 

Diphtheria. This disease is caused by bacteria which grow 
rapidly in the throat and form a false membrane there. But 
the most serious results come from the toxin, thrown off by the 
bacteria, which get into the blood and not only cause suffering 
and fever but also may have very serious after-effects on various 
body organs. As diphtheria is a throat disease, it may easily be 
conveyed from one person to another by the droplet method of 
infection. 

Other diseases spread through mouth spray. Influenza, pneu- 
monia, whooping cough, and certain kinds of colds, and many 
of the so-called children's diseases, are caused by bacteria or other 
microscopic organisms. Nearly all are spread by the " droplet 
method " of infection. In our army during the World War, 
influenza, coupled with pneumonia, was responsible for fourteen 
times as many deaths as were caused by shells and poison gases. 
This disease is periodically epidemic, the last bad outbreak pre- 
vious to this being in 1889. Influenza is apparently spread largely 
by human carriers, or people who have a slight attack but are 
capable of passing the disease on in its most serious form. 

Project. Use the report on infectious diseases, United States Public 
Health Reports, or your State Department of Health bulletin to deter- 
mine the decrease in typhoid in your state for the past ten years. 

Typhoid fever. Typhoid fever, not many years ago, was one 
of the most common germ diseases in this country and Europe. 
Today it is one of the less important of the communicable diseases. 
Typhoid bacilli multiply very rapidly in the intestine and are 
passed off from the body with the excreta from the food tube. 
If these bacilli get into the water supply of a town, an epidemic of 
typhoid will result. In one early epidemic in this country there 
were 5000 cases of typhoid in a city of only 30,000 inhabitants. 



WATER SUPPLIES 467 

Chicago and other cities which once obtained their drinking water 
from lakes polluted with sewage always had a high death rate from 
typhoid. In the year 1891, the death rate from typhoid was over 
170 per 100,000 inhabitants. Today it is less than 3 per 100,000. 
Olean, New York, had a serious outbreak of 248 cases in the fall 
of 1928 because one of the shallow wells used by the city became 
contaminated with sewage from the Allegheny River. It cost 
the city of Olean $425,000 to pay the cost of the care of the 
cases and to settle the claims made against the city for its care- 
lessness. 

Water supplies. By pure water we mean water free from all 
organic impurities, including disease germs. Water from springs 
and deep driven wells is the safest water ; that from large reser- 
voirs next best ; while water that has drainage in it, river water 
for example, is very unsafe unless properly treated with chemicals. 

The water from deep wells or springs, if properly protected, will 
contain few bacteria. Water taken from shallow, unprotected 
wells may have from 100 to 20,000 bacteria per cubic centimeter. 
Water taken from protected streams into which no sewage flows 
usually has few bacteria (from 50 to 300 bacteria per cubic centi- 
meter), and these are destroyed if exposed to the action of the 
sun and the constant aeration (mixing with oxygen) which the 
surface water receives in a large lake or reservoir. But water 
taken from a river into which the sewage of towns and cities flows 
may contain many hundreds of thousands of bacteria to the cubic 
centimeter,' and must be filtered and chlorinated before it is fit 
for use. The water is passed through settling basins and sand 
filters which remove about 98 per cent of the germs. Final treat- 
ment with hypochlorite of lime or liquid chlorine in very small 
amounts kills most of the remaining bacteria. A few fortunate 
cities, such as Los Angeles and New York, bring their water sup- 
plies from protected areas far up in the mountains. 

We have already seen the danger of typhoid fever from unpro- 
tected water supplies. Fortunately most large cities now protect 
their supplies, either by filtration and chlorination or, as in the 
case of Chicago, by this means plus a drainage canal which carries 
off the sewage. 



468 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



Practical Exercise 7. What methods of protection of water supplies are 
employed by your community ? Visit the city water supply and report on its 
conditions. Ask your teacher to give you references for Glenn's reports on 
the water systems of certain cities in this country. Report on some one 
system and compare it with your own city supply. 

Milk and disease. Another source of infection is milk. Fre- 
quently epidemics have occurred which were confined to users of 
milk from a certain dairy. Upon investigation it was found that a 
case of typhoid had occurred on the farm where the milk came from, 
that the germs had washed into the well, and that this water was 

used to wash the 
., -Q9\ milk cans. Once in 

,,--"*'* ~"-\ the milk, the bac- 

teria multiplied 
rapidly, so that the 
milkman gave out 
cultures of typhoid 
in his milk bottles. 
Most large cities 
now send inspectors 
to the farms from 
which milk is sup- 



®-"'(J 


P ^ 


p 


(3 


P $ 


p '"©... 


a 


P d 


p 


A 


\\ 


\ 
\ 


/ 


/ 
S / 




A. / 


\\ 


\ 



H^cCePark Dorchester "Milton. 

The small dots in the diagram show the number of cases of 
diphtheria which occurred in three towns, among people who re- 
ceived milk from dairy X. What may have been the reason 
for the cases of diphtheria which occurred in H of Milton ? 



plied. These men examine and score the health of the cows, the 
cleanliness of their surroundings, the health of the workers, the 
care and construction of the utensils, and the methods of handling 
the milk. Farms that do not attain certain standards of cleanli- 
ness are not allowed to have their milk become part of the city- 
supply. 

Care of a city milk supply. Besides caring for milk in its pro- 
duction on the farm, proper transportation facilities must be 
provided. Some of the milk used in Boston, Chicago, and New 
York is forty-eight hours old before it reaches the consumer. Milk 
used in the last-named city is said to come from eight states and 
from Canada. During shipment it must be kept in refrigerating 
cars, and during transit to customers it should be iced. 

Practical Exercise 8. What regulations are there in your community con= 
cerning the farms from which milk is supplied ? Concerning the sale of milk ? 
All but the highest grade milk should be pasteurized. Why? 



CARRIERS AND TYPHOID 



469 



Milk should be bottled by machinery, if possible, to insure no 
personal contact ; it should be kept in clean, cool places ; and no 
milk except that which is to be used for cooking should be sold 
by dipping it directly from cans. Why is this method of dis- 
pensing milk likely to contaminate it ? 



serving 
dish. B 



Project. Write or give a report in class on a visit to a dairy. 
Project. Investigate the sale of milk in your school and vicinity and 
report your findings to the class. 

Carriers and typhoid. A third and more serious method of 
spreading typhoid fever comes through " carriers." These are 
people who have 
had typhoid fever 
and who still harbor 
the living germs in 
their bodies. Sev- 
eral epidemics of 
typhoid have been 
traced to carriers 
who worked in 
dairies or on farms 
which produced 
milk. The well- 
known " Typhoid 
Mary" through her 
careless habits gave 
typhoid to people for 



\ (7 c^i ' 
food^^ handled 
by cool< 





fbocl. . 

by .'-tbeniffitep 




usecC 



y 






whom she cooked. 



The consumer is in danger of having his food and dishes con- 
taminated by the unclean hands of a worker. A line drawn 
Stil another i rom tne center circle to any of the persons, material, or 
utensils will mean eventual danger to the consumer. 

method of spreading 

typhoid is through carelessness in preparation of uncooked vege- 
tables. Several epidemics of typhoid fever have been traced to 
raw oysters which were " fattened " for the market in water that 
was contaminated with sewage. 

Laboratory Exercise. Plot curves from board of health tables to 
show the mortality from a certain disease during various seasons of the 
year. 

H. BIO — 31 



470 MAX CONTROLS HIS ENVIRONMENT FOR HEALTH 

Practical Exercise 9. Show how typhoid fever might be eradicated in this 
country. Think back to your general science work and show the different 
methods by which people can be protected from this disease. 

Septic sore throat. This disease is characterized by severe sore 
throat and fever, and is often followed by heart or kidney trouble. 
This is another disease carried by milk, and is caused by a strep- 
tococcus. The disease is probably given to cows by human 
beings who may be carriers. The cow may harbor the germ for 
several weeks and persons drinking unpasteurized milk from such a 
cow may take the disease. Several severe epidemics have been 
recorded, in Baltimore, Chicago, Lee, Massachusetts, in 1928, and 
other cities, but the worst was an outbreak of 2000 cases in 
Boston, in 1911. 

Tetanus. The bacillus causing tetanus is another toxin-forming 
germ. It lives in dust and dirt and is often found on the skin. 
It enters the body through cuts or bruises. It seems to thrive 
best in less oxygen than is found in the air. It is therefore im- 
portant not to use adhesive tape over wounds until they have 
been treated with antiseptics. The low death rate from tetanus in 
the World War was due largely to the fact that wounds were washed 
with powerful antiseptics and anti-tetanus serum was administered 
as soon as possible after the wounded were reached. 

Other diseases caused by bacteria. A group of bacteria which 
cause pneumonia, erysipelas, and other common infections besides 
septic sore throat are the so-called streptococci. Other coccus 
forms, the staphylococci (staf-i-16-kok'si), are responsible for boils 
and abscesses. A micrococcus causes one of the pernicious vene- 
real diseases, which produces terrible results. Other forms of 
micrococci probably cause cerebro-spinal meningitis (inen-in-jl'tis), 
formerly a fatal disease of the spinal cord but now often treated 
successfully with serums. Anthrax or splenic fever, Malta fever, 
whooping cough, bubonic plague, gas gangrene, one form of 
dysentery, cholera, and many other diseases are definitely associ- 
ated with specific forms of bacteria. In all of these diseases, 
contact with the person ill with the disease or, in some cases, 
with a carrier of the disease, is usually sufficient to cause its 
spread. 



REASONS FOR QUARANTINE 



471 



Practical Exercise 10. Make a table with the following headings and fill out 
for each disease mentioned in this unit. 



Disease 


Caused by 


Method of Transfer 


Prevention 











Self-Testing Exercise 

Raw milk is safe if it comes from (1) (2) cows 

and has careful (3). Infectious diseases are usually trans- 
mitted through (4) (5) . Bacteria usually enter the 

body through (6) (7) or breaks in the (8). 

(9) is gradually being conquered by proper treatment. 

Typhoid may be prevented through protection of (10) and 

(11) supplies, and detection and isolation of (12). 



PROBLEM IV. WHY IS QUARANTINE NECESSARY? 

Reasons for quarantine. We all know that when a person has 
a communicable disease, the doctor, acting under orders of the 
local board of health, puts the patient and sometimes the entire 
family under quarantine. Since this often seems needless, espe- 
cially if one has a mild attack of the disease, we ought to know the 
reason underlying such action. Communicable diseases become 
epidemic if they are not controlled. Measles, for example, is a dis- 
ease easily passed from one person to another. It is especially 
communicable among children, one of whom may have a very light 
case but may pass the germs to some one else who will have a 
severe attack of it. Scarlet fever, colds, and influenza are other 
diseases which are readily spread and may become epidemic. 
Since this is true, the reason for the isolation of the patient 
becomes evident. And every one should be unselfish enough to 
see this and to cooperate with the health authorities for the com- 
mon good of the community. 

The following table shows important facts about some common 



472 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



Disease 


Means op Communication 


Incubation Period (Approximate) and 
Early Symptoms 


Chicken pox . . 


Discharges from nose 
or throat of a pa- 
tient 


21 days. Rash. 


Diphtheria . . . 


Nose or throat dis- 
charges ; sometimes 
infected milk 


2 to 5 days. Begins like a cold. 


Measles .... 


Nose or throat dis- 


9 to 11 days. Begins like a cold. 




charges 


Reddish spots appear on the 
third day. 


German measles . 


Nose or throat dis- 


Unknown, though longer than 




charges 


measles. 


Mumps .... 


Nose or throat dis- 


Unknown, probably about 2 




charges 


weeks. Pain in salivary glands. 


Infantile paralysis 


Nose, throat, or bowel 


Not known. Fever, headache, 




discharges of pa- 


vomiting, weakness of one or 




tient or carrier 


more muscle groups. 


Scarlet fever . . 


Discharges from nose, 


2 to 7 days. Begins like a cold ; 




mouth, ears. In- 


in 24 hours evenly diffused 




fected milk 


bright red spots under skin. 


Smallpox . . . 


All discharges of a 


About 12 days. Fever and back- 




patient ; particles 


ache. Red shotlike pimples on 




of skin and scabs 


face and hands, become blisters. 


Septic sore throat 


Discharges from nose 
or mouth 


Varies with resistance. Short. 


Whooping cough . 


Discharges from nose 


14 days. Cough worse at night. 




or mouth 


"Whooping" develops in about 
two weeks. 



Incubation period of disease. Quarantine regulations often 
affect not only the person having the disease, but also all those of 
the family who were " exposed " ; that is, who came in personal 
contact with the person who has the disease. If, for example, you 
have measles, the doctor will keep at home the other children in 
the family who have not had the disease. The period of quaran- 
tine for measles lasts in most states fifteen days. Why this pre- 
caution? 

Consider what we already know of germs. We found it took a 
certain length of time for colonies of germs to appear in a culture 
medium after exposure. In the same way it takes a certain 
amount of time in the case of a disease for the germs to become 
so abundant in the body that they give off sufficient toxins to 



INCUBATION PERIOD OF DISEASE 



473 



cause the symptoms of the disease. This period, between the 
time when the germs enter the body and the time the symptoms of 
disease appear, is called the incubation period. Since this period 



a neighbor- and 
playmate Gpn 22 
quarantined 
for- measles 



a .school chum, 
not at par t>^ 
quarantined 
vi tte rr}easksAprr20 



party held" Apn 8 
at Valentine borne. 
AprrloJanetVthe 
l205tess" developed 
measles 



Apr: 21 Dorothy 
5. quarantined 
with rrceasles- 
gaest at party 



Patty and £ lien 5. 



i/ith measles 



Apn24"MaryTT 
quarantined 
>xdth measles - 
guest at party 



Two days after her party Janet developed measles. Since she was not ill with the disease 
at the time of the party, how do you account for the other cases which developed? 

varies for different diseases, the period of quarantine also varies, 
as seven days for scarlet fever, fourteen days for whooping cough, 
twenty-one days for chicken pox. If, after one has been exposed 
to an infectious disease, no symptoms develop within the time of 
the recognized incubation period, it is safe to assume that he will 
not get the disease. 

Practical Exercise 11. Study the diagram. How have similar cases worked 
out in your own school? Diagram them. 

Why is it necessary for protection of others to know the incubation period of 
a disease? 

Practical Exercise 12. Why should persons ill with an infectious disease 
be isolated until they are well? What methods has the Board of Health for 
warning strangers of the presence of the disease in a home ? 

What is the reason for quarantine and by what should it be followed to be 
effective ? Why is there a quarantine station at the entrance of San Francisco, 
Boston, or New York harbor? Why is it of particular value there? 

Practical Exercise 13. What do we mean by disinfection? What are the 
rules of your local Board of Health in regard to disinfection. 

What should be done to the body, clothing, and hair of a person who has 
been ill with an infectious disease before he is allowed to go among well persons 
again? Why is this necessary? 

Can a person have the germs of a disease in the body and still not show 
symptoms of the disease? How might such a person be a danger to others? 



474 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

Self-Testing Exercise 
Check the correct statements for your workbook : 

T. F. 1. The incubation period of a disease is the period between 
the time the germs causing the disease enter the body and the symp- 
toms of the disease appear. 

T. F. 2. All communicable diseases have the same length incuba- 
tion period. 

T. F. 3. Children who have been exposed to a catching disease 
should remain at home during the incubation period. 

T. F. 4. Communicable diseases do not become epidemic. 

T. F. 5. Quarantine means the isolation of a person who has a 
communicable disease. 

T. F. 6. The length of quarantine differs with different diseases. 

T. F. 7. Epidemics cannot be prevented. 

T. F. 8. We only catch a disease from people suffering from that 
disease. 



PROBLEM V. WHAT IS IMMUNITY? 

The meaning of immunity. It is a matter of common knowl- 
edge that some persons in a family will have a very light attack of 
a communicable disease, while others may have it severely. Some 
one else may be exposed again and again to this same disease and 
not take it, because he is immune to, or able to resist, that particu- 
lar disease, while those who take it are susceptible to its attack. 
Immunity against disease may be individual, or it may be racial. 
Negroes, for example, are very susceptible to measles and tuber- 
culosis, but are less susceptible than white people to malaria, yel- 
low fever, and smallpox. There are also great differences as to 
the degree of immunity from the same disease in different species 
of animals. Tuberculosis of the bovine type may occur in chil- 
dren as well as in cattle, hogs, and horses. The human tubercu- 
losis germ attacks only guinea pigs, monkeys, and man. Smallpox 
and cowpox are probably caused by different types of the same 
organism. Plague attacks rats, ground squirrels, mice, and guinea 
pigs, as well as man. A long series of laboratory tests show that 
most germs that cause illness in man develop ordinarily in man 



ACQUIRED IMMUNITY 



475 



only, while a few diseases, like anthrax and glanders, are primarily 
diseases of certain animals but may attack man. 

Immunity may be modified by external conditions. A certain 
amount of immunity is evidently natural to individuals, races, or 
species, but there is much variation, as we have seen, even among 
individuals of the same family. Resistance to disease also is 
modified by the condition of the individual exposed. Overworked, 
tired, and " run-down " persons are much more likely to take 
diseases than those who are in good physical trim. Resistance to 
disease may also be weakened by the use of drugs and alcohol 
as shown by the susceptibility of heavy drinkers to pneumonia. 

Acquired immunity. It has been a matter of common knowledge 
for centuries that persons who once have infectious diseases do not 
usually have them 
a second time. A 
Greek historian, de- 
scribing a visitation 
of plague in Athens, 
more than twenty 
centuries ago, noted 
that those who had 
plague and recovered 
were safe from it 
thereafter. The 
Chinese, in order to 
make their children 
immune to smallpox, 
gave them the dis- 
ease in a mild form 
by placing in the 
nose a little of the 
pus from one of the 
eruptions. It was the chance statement of a dairymaid in Eng- 
land when she said, " I've had cowpox and can't take smallpox," 
that led Edward Jenner to make his first experiments that have 
resulted in almost stamping out smallpox through vaccination. 
And so today when we think of acquired immunity obtained by 




l a. tier Service 
The first vaccination against smallpox by Dr. Jenner. 



476 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

this or that antitoxin or anti-serum or vaccine, we must remember 
those pioneers, Jenner and Pasteur, who took the first steps in 
controlling germs, and began the work which may result finally 
in preventing many diseases. 

How the body protects itself. We have already learned that 
the blood contains small amounts of various protective sub- 
stances, known collectively as antibodies. These help the cells of 
the body combat harmful bacteria, the poisons or toxins which the 
bacteria give out, and the poisonous " split proteins " which are 
thrown into the blood when these bacteria die. When any protein 
substance decays, or is only partly digested, it breaks down into 
simpler substances. Some of these simpler proteins are poisonous 
and are called ptomaines (to'ma-mz ; Gr. ptoma, dead body). 
Ptomaine poisoning, while not so common as was once thought, 
sometimes causes discomfort and even death. 

Practical Exercise 14. With the help of a physician, list all the diseases 
for which immunity has been developed. 

Practical Exercise 15. What is immunity? Why are some persons more 
likely to take a disease than others? Why do some people have a disease more 
severely than others ? Why does travel bring increased likelihood of disease ? 

Self-Testing Exercise 
Check the correct statements for your workbook : 

T. F. 1. A person is immune to a catching disease if, when ex- 
posed to it, he does not take it. 

T. F. 2. Negroes are much more susceptible to measles and 
tuberculosis than white people. 

T. F. 3. The resistance to a disease is largely determined by a 
person's physical condition. 

T. F. 4. Protective substances, antibodies, in the blood help the body 
to combat bacteria and their poisons. 

T. F. 5. Toxins are useful substances in the blood which help keep 
us well. 

PROBLEM VI. WHAT ARE THE DIFFERENCES BETWEEN 
ACTIVE AND PASSIVE IMMUNITY? 

Active and passive immunity. All toxins, when they enter the 
human body, cause the body cells to react to the poison. If the 



ANTITOXINS 



477 



cells are able to manufacture the protective substances, antibodies, 
rapidly enough to counteract the work of the bacteria or their 
poisons, we recover from the disease. In such a case as this, the 



■Crisis 



onset-* 



convalescence 




periocC of 
incubatiora 



jpection 



. perioct 
ofimmurnit^ 

Read your text, study the diagram carefully, and then explain how the body produces an 
immunity against a specific disease. 

body cells do the work in righting the disease, and the immunity 
thus acquired is said to be active. In case the body cells themselves 
do not work, and, instead, an antitoxin is used, which is manufac- 
tured outside the body, we have an example of passive immunity. 
Let us consider the latter case first, as it is easier to understand. 

What are antitoxins and how are they used ? An example of 
passive immunity is that obtained by the antitoxin treatment for 
diphtheria. This treatment, as 
the name denotes, is a method 
of neutralizing the toxin given 
off by the bacteria into the body. 
It was discovered by a German, 
Von Behring r that the serum of 
the blood of an animal immune 
to diphtheria is capable of neu- 
tralizing the poison produced 
by the diphtheria-causing bac- 
teria. Horses develop large 
quantities of antitoxin when 
given the diphtheria toxin in 
gradually increasing doses. 



day 
1st, 

2nd 

3rd 

4rtfe 

5th 


deaths "per- loo cases 

none 


SI 




II 1 




IS. 1 




» ■■■■■■'■■: I 





The early use of antitoxin in cases of diph- 
theria greatly decreases the death rates from 
this disease. 



478 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 




SdtLcrteCit y 



since 1927 
20.000 of thev 
co.500 children 
immunised 



The serum of the blood of these horses is then carefully tested 
and is used to inoculate the patient suffering from or exposed to 
diphtheria, and thus the disease is checked or prevented alto- 
gether. The laboratories of boards of health prepare this antitoxin 
and supply it fresh for public use. 

It has been found from experience in hospitals that deaths from 
diphtheria are largely preventable by the early use of antitoxin. 
It is therefore advisable, in a suspected case of diphtheria, to have 
antitoxin used at once. 

Schick test and its value. By the Schick test it is possible to 
determine if a person is immune to diphtheria. A very minute dose 

of diphtheria toxin 
is injected under the 
skin of the forearm. 
If the person is im- 
mune, no reaction 
takes place, because 
the blood is provided 
with antitoxins. But 
if the person is sus- 
ceptible, some hours 
later a slight red spot 
appears where the 
toxin was injected. 
This is a danger 
signal and shows that 
the person would take 
diphtheria if exposed to it. To such a person a treatment, known 
as the toxin-antitoxin treatment, is given. Small amounts of a 
mixture of diphtheria toxin and antitoxin are injected into the 
susceptible person, with the result that he becomes immune by 
a combination of active and passive immunity. This treatment 
has been tried with thousands of school children in the city of New 
York, with the result that the death rate from diphtheria dropped 
lower than before its use. 

The following clipping from a New York paper indicates the 
progress made in wiping out this dread disease. 



1902 - 1922 1924 '25 '26 27 '2S '29 30 
reportecC Cases 165 199 269 297 86 60 23 



200 



How does this diagram show the value of giving children toxin- 
antitoxin to prevent diphtheria ? 



ANTITOXINS 479 

" Quoted as an evidence of the efficacy of inoculation against diph- 
theria, the statement is made that there were 2226 fewer cases of 
diphtheria in New York in 1929 than there were in the preceding year. 
The number of those dying from the disease here last year was 180 
less than the number who died of it in 1928. 

" More than 700,000 children received the toxin-antitoxin treatment 
during the year, making them immune from what not many years 
ago was a scourge. Approximately 10,000,000 pieces of educational 
literature, printed in eleven languages, were distributed during the 
year. The progress made in recent years has warranted the prediction 
that in five years the disease will be exterminated." 

The Dick test and treatment promise to do as much in combating 
scarlet fever as the Schick test has done in reducing the death rate 
from diphtheria. In the Dick test a diluted toxin produced by 
the bacteria which cause scarlet fever is injected into the arm. A 
redness indicates that the person is susceptible to scarlet fever. 
Treatment is then given in the form of subsequent doses of toxin 
which helps the body to produce its own antitoxin and thus build 
up an active resistance against the disease. 

Other antitoxins. Tetanus, commonly called lockjaw, once 
a much-dreaded infection, has now been almost stamped out 
through the use of a tetanus antitoxin. During the World War 
soil-infected wounds were treated with this antitoxin and as a 
result the death rate from tetanus was much lower than in previ- 
ous wars. An antitoxin was also used successfully against gas 
gangrene. Antitoxins are also used for certain types of dysentery 
and against snake venoms. 

Active immunity. Vaccination against smallpox. In 1796 Jen- 
ner first proved that inoculation with pus taken from a cow was 
capable of preventing smallpox. Years later Louis Pasteur proved 
that inoculation of chickens with an old weakened culture of chicken 
cholera bacteria caused the chickens to be slightly ill for a short 
time, but made them immune to chicken cholera. Their body cells 
were stimulated by the weakened germs to manufacture antibodies 
which soon got the better of the germs and provided immunity. 

So it is with vaccination against smallpox. Smallpox is caused 
by a filterable virus which means the organisms are too small to 



480 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

be seen with the most powerful microscope. The virus used for 
inoculation probably contains the organisms which cause cowpox, 
which is a weakened smallpox organism. Therefore when vacci- 
nation " takes," the body has been stimulated by the virus to 
produce its own antibodies. These antibodies make the body 
actively immune to the disease. 

Smallpox has been in the past a great scourge ; 90 out of every 
100 persons in Europe used to have it. As late as 1898, in Russia 



1921 1922 1923 192419251926192719281929 1930 I 1921 1922 1923 1924 1925 1926 1927 1929 1929 1930 

deaths 000200001 o deaths 20 l .56 5B 236 5 2 10 7 



Massachusetts 



Cases. « 2 6 12 3 4 2 19 273 2 cases 
repor ted . ■ 

1921 192219231924192519261927192819291930 I 1921 1922 1923 192419251926 192?192S1929 1930 




Massachusetts has a law requiring all persons to be vaccinated against smallpox infection. 
California, at one time, had such a law, but repealed it. Notice the number of cases and deaths 
from smallpox in California as compared with Massachusetts from 1922 to 1930. 



over 50,000 persons lost their lives from this disease in a year. 
In some places smallpox has been brought under absolute control 
by vaccination, though in other places, unfortunately, there are 
outbreaks, due to the fact that some people do not believe in 
vaccination. 

Rabies, or hydrophobia. Rabies (ra/bi-ez), which is caused by 
a filterable virus, is communicated in the saliva from one dog to 
another by biting. It is also transmitted to man by the bite of an 
infected animal. The great French bacteriologist, Louis Pasteur, 
discovered a method of treating this disease which is a success if 
begun soon after the person has been bitten by the infected 
animal. Here again the treatment is based upon the inocu- 
lation of the patient with a weakened organism which causes 



THE. MECHANISM OF ACTIVE IMMUNITY 481 

the body cells to set up a resistance and produce an active 
immunity. 

Vaccination against typhoid,, The principle underlying vacci- 
nation against typhoid is that of working up an active immunity 
by introducing into the body large numbers of dead typhoid germs. 
The presence of the dead bacilli stimulates the blood to make 
antibodies and thus an active immunity is acquired. This im- 
munity protects the person against the invasion of living germs. 

During the Spanish-American War in the army of 107,000 men 
more than 20,000 were disabled with typhoid. Since 1914, after 
vaccination against typhoid was introduced, the disease has been 
almost stamped out in the army, and the death rate for the entire 
country has been so much reduced that it is now a disease of 
relatively little importance. 

The Widal test, by means of which it is possible to determine at 
once whether a person has typhoid, has been described on page 390. 

The mechanism of active immunity. Active immunity is 
thus brought about in a number of different ways : by the intro- 
duction of living organisms, by the introduction of attenuated or 
weakened organisms, by the introduction of dead organisms, and 
by the introduction of extracts containing the products of bacteria. 
All of these substances may be called vaccines. 

The underlying principle is the same in all cases ; certain cells of 
the body are roused or activated to form antibodies, and the invad- 
ing organisms are destroyed and their toxins neutralized. These 
conditions are brought about through the work of the lysins, 
precipitins, agglutinins, opsonins, and phagocytes already men- 
tioned in Unit XIII. You should read that unit carefully again 
in connection with the present unit. 

Other vaccines are made and used successfully against boils, 
another against paratyphoid, and still others for plague and for 
cholera. When tests show sensitiveness to certain pollens, serums 
are made from them and a certain amount of immunity from 
hay fever is thus received. But we are just at the beginning of 
discoveries along this line and it will no doubt be the work of the 
physicians and scientists of the future to perfect many more ways 
of producing immunity against protein poisons and germ disease. 



482 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

Practical Exercise 16. Study the diagram on page 480. Show exactly why 
the changes noted there occurred. 

Practical Exercise 17. What is the principle underlying the antitoxin 
treatment for diphtheria? The Schick test? The Dick test? What is the 
principle underlying vaccination against smallpox ? Against typhoid ? Against 
boils? Explain. 

Practical Exercise 18. Make a list of all germ diseases that are now treated 
by the passive method of immunity ; the active method of immunity. 

Positive health the goal. In the preceding pages we have seen 
what science has done in combating disease. But many of these 
diseases can be avoided simply by keeping in good condition. 
If we keep our bodies in good physical condition through the use 
of proper food, exercise, and sleep ; if we maintain a calm poise 
and untroubled mind ; if we avoid worry and are cheerful in spite 
of difficulties ; then we have gone far toward keeping well. We 
now have the knowledge about communicable diseases and how to 
fight them ; let us use this knowledge if it is necessary. But for 
most of us health is something that can be earned, if we are willing 
to pay the price. All that we have to do is to treat our bodies in 
such a way that they will give us the most efficiency, for very few of 
us have really poor bodily machines to start with. 

Self-Testing Exercise 

When poisons enter the body, the cells react by forming 

(1). The two kinds of acquired immunities are (2) 

and (3) . In the first, immunity is acquired through the 

use of (4) ; and in the second through the use of (5). 

The Schick test is used to determine whether a person is (6) 

to (7). This disease may be eradicated by the use of 

(8). Diseases that may be stamped out by the use of 

vaccination are : (9), (10), ......... (11), and 

(12). 

PROBLEM VII. HOW IS MALARIA CAUSED AND 
TRANSMITTED? 

The cause of malaria. The study of the life history and the 
habits of the Protozoa has resulted in finding many parasitic 
forms, and the consequent explanation of some diseases. An 
amoeba-like parasite, of which at least three species exist, causes 



CAUSE OF MALARIA 



483 




different types of malaria. This disease, not many years ago, was 
thought to be caused by bad air. (Hence the name, from Italian 
mala, bad ; aria, air.) But the work of a number of scientists 
has shown that the disease is carried by a mosquito and is caused 
by an amoeba-like organism, called Plasmodium malariae. When 
a female mosquito of the 
species Anopheles (a-nof 'e- 
lez) sucks blood from a 
person having malaria, 
this parasite passes with 
the blood into the stomach 
of the mosquito. After 
about twelve days in the 
mosquito's body, the 
parasites, having passed 
through the sexual stages, 
establish themselves 
within the salivary glands 
of the mosquito. If the 
infected mosquito then 
bites a person, it passes 
the parasites into the 
human blood with its 
saliva. These parasites 
enter the corpuscles of 
the blood, increase in size, 
and then form spores. 
The rapid process of spore 
formation results in the 
breaking down of the blood corpuscles. The spores then escape 
into the blood stream. The sudden release of the spores and the 
poisons are thought to cause the chills and the fever so character- 
istic of malaria. The escaped parasites may enter other blood 
corpuscles and in forty-eight or more hours, depending on the kind 
of malaria, repeat the cycle. The spores feed upon the red 
corpuscles, and destroy half or even four fifths of the normal 
number. This accounts for the pale, anaemic condition of a person 



The malarial parasite passes its life cycle from a 
mosquito, to man, and back again to a mosquito. 
Trace the life history of the parasite in the above 
diagram. 



484 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

who has malaria. The only cure for the disease is frequent doses 
of quinine. This kills the parasites in the blood. 

Workbook Exercise. Using the text and diagram, work out a life 
cycle of the malarial parasite. 

Demonstration 4. To show life history of a mosquito. 

Use charts or material in Riker mounts, to show history of any mosquito. 

The malarial mosquito. Fortunately for mankind, not all 
mosquitoes harbor the parasite which causes malaria. The harm- 
less mosquito {Culex) may be usually distinguished from the mos- 
quito which carries malaria (Anopheles) by the position of the body 
and legs when at rest. Culex lays eggs in tiny rafts of one hundred 





acCult cccCult 

How does the common mosquito, Culex (on left), differ in the various stages of growth from the 
malarial mosquito, Anopheles (on right) ? 

or more in standing water ; thus the eggs are distinguished from 
those of Anopheles, which are not in rafts. Rain barrels, gutters, 
and old cans may breed in a short time enough mosquitoes to 
annoy a whole neighborhood. The larvae are known as wigglers. 
They appear to hang on the surface of the water, head down, in 
order to breathe through a tube at the posterior end of the body. 
In this stage they may be recognized by their peculiar movement 
when on their way to the surface to breathe. The pupa, dis- 
tinguished by a large head and thoracic region, breathes through 
a pair of tubes' on the thorax. 



EXTERMINATION OF MOSQUITOES 



485 



Practical Exercise 1">. Use the diagram and compare the life histories of 
the Anopheles and Culex so that you can determine the harmful form at any 
stage in its life history. 

How may mosquitoes be exterminated? The fact that both 
larvae and pupae take air from the surface of the water makes it 
possible to kill the mosquito during these stages by pouring oil 
on the surface of the water where they breed. The introduction of 




U. S. Department of Agriculture 

Dusting with Paris green from an airplane to destroy the malarial mosquito larvae on the 
surface of water in the swamp and lake. 

minnows, goldfish, or other small fish where the mosquitoes breed 
will do much in freeing a neighborhood from this pest. Draining 
swamps or low land which holds water after a rain is another 
method of extermination. Since the beginning of historical times, 
malaria has been prevalent in regions infested by mosquitoes. 
The ancient city of Rome was so greatly troubled by periodic 
outbreaks of malarial fever that a goddess of fever came to be 
worshiped in order to lessen the severity of what the inhabitants 
believed to be a divine visitation. At the present time malaria 



H. BIO- 



32 



486 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

is being successfully fought and conquered in Italy by the draining 
of the mosquito-breeding marshes. 

The problem of malaria affects nearly 13,000,000 of the inhabit- 
ants of the United States, principally those of the southern states. 
Mississippi, with over 92 per cent of its population, shows a death 
rate of over 10 deaths per 100,000 from malaria ; Florida with 80 
per cent of her population exposed to malaria, and Arkansas, 
with 75 per cent living in malarial districts, present the most 
serious problems from a health standpoint. In Arkansas, Mis- 
sissippi, and other southern states successful fighting of malaria 
by draining marshes, oiling standing water, and screening houses 
has greatly reduced the number of malarial patients. 

Project. To make a survey of your neighborhood to determine if 
there are any breeding places for mosquitoes. How can these places 
be reduced? 

Other protozoan diseases. Many other diseases of man are 
probably caused by parasitic protozoans. Dysentery of one kind 
is caused by the presence of an amoeba-like animal, Endamoeba, 
in the digestive tract. These parasites are far more widely spread 
than was ever thought and many people suffer from the effects of 
this parasite without knowing what 'actually causes them to be ill. 

Another group of protozoan parasites are called trypanosomes. 
These are parasitic in insects, fish, reptiles, birds, and mammals 
in various parts of the world. They cause several diseases of 
cattle and other domestic animals, being carried to the animal in 
most cases by flies. One of this family is believed to live in the 
blood of native African zebras and antelopes. Seemingly it does 
them no harm, but if one of these parasites is transferred by the 
dreaded tsetse (tse'tse) fly to one of the domesticated horses or 
cattle of that region, the animal dies. 

The tsetse fly also carries to the natives of Central Africa a 
trypanosome which causes the dreaded and incurable sleeping 
sickness. This disease has killed more than fifty thousand 
natives yearly, and many Europeans have succumbed to it. Its 
ravages are largely confined to an area near the large Central Afri- 
can lakes and the upper Nile, for the fly which carries the disease 



YELLOW FEVER 487 

lives near water, seldom going more than 150 feet from the banks 
of streams or lakes. The British government has attempted to 
control the disease in Uganda by moving all the villages at least 
two miles from the lakes and rivers. Among other diseases that 
may be due to protozoans is kala azar, a fever in hot Asiatic 
countries which is probably carried by the bedbug, and African 
tick fever, carried by a small insect called the tick. In this 
country many fatal diseases of cattle, as " tick fever," or Texas 
cattle fever, are caused by protozoa. 

Self-Testing Exercise 

Malaria is caused by a (1) which is carried by the 

(2) (3). It lives part of its life in the body of the (4) 

and part in . . •. (5). When the (6) bites a person, it 

passes the (7) into the (8) with its saliva. Malaria 

can be eradicated by (9) the (10) (11) of 

(12). Other diseases probably caused by protozoans are 

(13), (14) (15), (16), and 

(17) (18). 

PROBLEM VIIL HOW WAS THE CAUSE AND CONTROL OF 
YELLOW FEVER DISCOVERED? 

Yellow fever and mosquitoes. Another disease carried by 
mosquitoes is yellow fever. In the year 1878 there were 125,000 
cases and 12,000 deaths in the United States, mostly in Alabama, 
Louisiana, and Mississippi. During the French attempt to con- 
struct the Panama Canal, the work was at a standstill part of the 
time because of the ravages of yellow fever. Before the war with 
Spain, thousands of people were ill in Cuba. But today yellow 
fever has almost disappeared, both there and in the Canal Zone, 
through proper control of the fever-carrying mosquito Aedes. 

The knowledge that Aedes carries the disease-producing agent 
that causes yellow fever is due to the experiments in 1900 of a 
commission of United States army officers, headed by Dr. Walter 
Reed. One of these men, Dr. Jesse Lazear, lost his life in an ex- 
periment to prove that yellow fever is transmitted by mosquitoes. 



488 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

He allowed himself to be bitten by a mosquito that was known 
to have bitten a yellow fever patient, contracted the disease, and 
died a martyr to science. Others, soldiers, volunteered to test 
further by experiment how the disease was spread, so that in the 
end the commission was able to prove that Aedes transmitted yel- 
low fever. The accompanying illustration shows the result of this 



3S5T y^ 19 °° 


year 190i 


500 


























1 


i i i 




"100 
























/ 


antirmosquito 
! campaign begZxn 




100 
















\ 




/ 


/ 


/ 

































\ 


< 


/ 




















api:>fayJura July O^.Sept.Q:t.>lov:Dee. Jan ."feb. Mac ApchbyJitDe MyAug.5eft0ct}k\/&c. 



In 1900, experiments were carried on to find the cause of yellow fever. In 1901, it was dis- 
covered that the Aedes mosquito transmitted yellow fever and a campaign against mosquitoes 
was immediately started. The above chart shows the effect of such a campaign in Havana. 

discovery for the city of Havana. For years Havana was con- 
sidered one of the pest spots of the West Indies. When Americans 
occupied that city, after the war with Spain, they cleaned up the 
city, introduced proper sanitation, placed screens in most build- 
ings, and so nearly destroyed the breeding places of the mosquitoes 
that the city was practically freed of mosquitoes. The result, so 
far as yellow fever was concerned, was startling, as you can see by 
reference to the chart. 

Practical Exercise 20. Read the Health Heroes Series by Hallock and Tur- 
ner, and make a report to the class on yellow fever. 



Self-Testing Exercise 

A commission headed by Dr (1) proved that the Aedes 

mosquito carries (2) (3). This disease was elimi- 
nated in Havana by (4) the (5) (6) of 

mosquitoes, (7) the buildings, and introducing (8) 

(9). 



THE HOUSE FLY 



489 



PROBLEM IX. WHAT ARE OTHER DISEASE CARRIERS AND 
WHAT DISEASES DO THEY CARRY? 

Demonstration 5. Observe the foot of a house fly under a com- 
pound microscope. Why it is able to carry bacteria. 

Allow a fly to walk across a sterile agar plate. Cover the plate and 
set it aside in a warm place for several days. Describe the plate. 

Demonstration 6. The life history of the typhoid fly. 

Expose pieces of raw beef where flies will light on them. After a 
few hours, cover this meat in glass dishes or small battery jars with 
screen covers. 

Watch the meat. In pieces on w T hich eggs were laid by the flies 
describe the stages of development as they appear. Do the larvae 
grow? They are called maggots. State how the pupae differ from 
the larvae. Watch to see the adults emerge from the pupal case. 

How long does a complete life history take ? How many generations 
of flies might develop during a hot summer? 

The house fly. We have already learned that mosquitoes of 
different species carry malaria and yellow fever. Another addition 
to the black list of disease-carriers is the house or typhoid fly. The 
development of the 
house fly is extremely 
rapid. A female may 
lay from one hundred 
to two hundred eggs 
at one time. These 
are usually deposited 
in filth or manure. 
Dung heaps about 
stables, outdoor toilets, 
neglected garbage 
cans, and fermenting 
vegetable refuse form 
the best breeding 
places for flies. In 
warm weather, the eggs 
hatch a day or so after they are laid and the larvae or maggots 
crawl out. After about one week of active feeding these wormlike 
maggots become quiet and go into the pupal stage, whence under 
favorable conditions they emerge within less than another week as 
adult flies. The adults breed at once, and in a short summer 



1 




s 


mm ** "' ' ¥ mw% 



Paul Griswold Howes 

A blue-bottle fly depositing eggs in the bill of a dead starling, 
which will furnish food for the young larvae. 



490 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



there may be over ten generations of flies. This accounts for the 
great number of flies in July and August. Fortunately, rela- 
tively few flies survive the winter. 

The foot of the fly shows a wonderful adaptation for clinging to 
smooth surfaces. Two or three pads, each of which bears tubelike 

hairs that secrete a 
sticky fluid, are found 
on its under surface. 
It is by this means that 
the fly is able to walk 
upside down, and carry 
filth and bacteria on its 
feet. 



claw mom TIP OF FOOT 




Foot of a house fly. 



Amer. Mus. of Nat. Hist. 
Why is the fly a carrier of diseases? 



Project. To determine 
the breeding places of 
flies in your neighbor- 
hood. 

The house fly a dis- 
ease carrier. The com- 
mon fly is recognized 
everywhere as a pest. 
Flies have long been known to spoil food through their filthy 
habits, and they are blamed for spreading several diseases caused 
by bacteria. It has been found that a single fly might carry on 
its feet anywhere from 500 to 6,600,000 bacteria, the average 
number being over 1,200,000. Not all of these germs are harm- 
ful, but they might easily include those of typhoid fever, tuber- 
culosis, " summer complaint," and possibly other diseases. A 
pamphlet published by the Merchants' Association in the city of 
New York shows that the rapid increase of flies during the summer 
months has a definite correlation with the increase in the number 
of cases of ' ' summer complaint. ' ' Observations in other cities seem 
to show that the increase in the number of typhoid cases in the 
early fall is due, in part at least, to the same cause. 

Project. If vital statistics of your community are available, work 
out a correlation between the increase of flies and the increase of 
certain diseases. 



DISEASE CARRIERS 



491 



Cleanliness which destroys the breeding places of flies, the 
frequent removal and destruction of garbage, rubbish, and manure, 
the covering of all food when not in use, and especially the careful 
screening of windows and doors during the breeding season are 
wise precautions taken to prevent the spread of diseases by flies. 
Far more important than to " swat the fly "is to remove their 
breeding places ! 

Practical Exercise 21. What is the best method for destroying flies in your 
home? Knowing when and where flies breed, when would be the best time 
to " swat the fly "? How would this method compare with other ways of 
extermination ? 



Other insect disease carriers. Fleas and bedbugs have been 
added to those insects proved to carry disease to man. Bubonic 
plague, which is primarily a disease of rats, is transmitted from 
infected rats and ground squirrels to man by fleas. Fleas are also 
believed to transmit from rats to rats a form of leprosy found only 
in these animals. It 
is thought probable 
that bedbugs trans- 
mit relapsing fevers. 
Typhus fever is 
transmitted by body 
lice. 

Animals other than 
insects that may 
spread disease. The 
common brown rat 
is an example of a 
mammal, harmful to 
civilized man, which 
has followed in his 
footsteps all over the 

world. Starting from China, it spread to eastern Europe, thence to 
western Europe, and in 1775 it had arrived in this country. In 
seventy-five years it reached the Pacific coast and it is now fairly 
common all over the United States, being one of the most prolific 
of all mammals. Rats spread bubonic plague, the " Black Death " 




ground. 
Scjuirrel 



Boccillusr 

\ 

man 



nf 



; 



Explain from the diagram, how the bubonic plague is carried? 



492 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

of the Middle Ages, a disease estimated to have killed 25,000,000 
people during the fourteenth century. Fleas bite the infected 
rat and then transmit the disease to man. In 1900 the plague 
gained entrance on our western coast. It killed more than 100 
persons during the next four years, and small outbreaks have 
occasionally occurred ever since. The ground squirrels of Cali- 
fornia became infected with the plague, doubtless from the rats 
which lived in their burrows, so that now the danger of other out- 
breaks of the plague will be present until all the ground squirrels 
are exterminated. Over a million rats were killed in fighting the 
last outbreak of bubonic plague in California and efforts are being 
made in all large cities to eradicate this pest. 

Practical Exercise 22. Look up Farmers Bulletin 896 and report on the 
best way to exterminate rats. 

Project. Make a survey of your neighborhood to determine where 
rats breed. 

Self-Testing Exercise 

The house fly may carry (1) and (2) bacteria 

on its feet. It breeds (3) in (4) (5) during 

the warm season. Fleas are carriers of (6) (7), 

which they get from (8) (9) and (10) 

(11). This disease can be eradicated by exterminating all 

(12) and (13). Body lice transmit (14) 

(15). 



PROBLEM X. WHAT DISEASES ARE CAUSED BY WORMS 
AND HOW MAY WE FIGHT THEM? 

Other parasitic animals cause disease. Other animals besides 
those mentioned have been found to cause illness. Chief among 
these are certain roundworms and flatworms, which live as parasites 
not only in man but in many animals and plants. The parasite 
frequently becomes fastened to its host during adult life and is 
reduced to a mere bag through which the fluid food prepared by its 
host is absorbed. Sometimes a complicated life history results 
from parasitic habits. Such is the life history of the tapeworm 
and of the liver fluke, a flatworm which kills sheep. 



TAPEWORMS 



493 



infectecC 
Small f'eh^ 




segments 
iJreaJt off 
appear- m 
feces 



tape*£n*m, 
in the*, 
intestine 



^egm-ants 
liberate 
mariv- egg's 



g^- ; - ^ « at (Xclops" 



Cestodes or tapeworms. These parasites infest man and many 
other vertebrate animals. One tapeworm (Taenia solium) passes 
through two stages in its life history, the first within a pig, the 
second within the intestine of man. The developing eggs are 
passed off with wastes from 
the intestine of man. The 
pig, an animal with dirty 
habits, may take in the 
tapeworm embryos with its 
food. These develop within 
the intestine of the pig, but 
scon make their way into 
the muscles or other tissues, 
where they are known as 
bladder worms. If man 
eats undercooked pork con- 
taining them, he is likely to 
become a second host for 
tapeworms. 

Another common tape- 
worm ( Taenia saginata) 
parasitic on man lives part 
of its life as an embryo 
within the muscles of cattle. 
The adult tapeworm con- 
sists of a round headlike 
part provided with hooks, 
by means of which it fastens itself to the wall of the intestine. 
This head now buds off a series of segment-like structures, which 
are practically bags full of sperms and eggs. These structures, 
called proglottids, break off from time to time, thus allowing the 
developing eggs to escape. The proglottids have no separate 
digestive systems, but the whole body surface, bathed In digested 
food, absorbs it and thus they are enabled to grow rapidly. 

Roundv/orms. Still other wormlike creatures called round- 
worms are of importance to man. Some, as the vinegar eel found 
in vinegar, or the pinworms parasitic in the lower intestine, partic- 








Cyclops <lcct «gg> 

George W. Hunter III 

The bass tapeworms infest the small-mouthed black 
bass. The mature posterior segments of the worm, 
filled with eggs, break off and pass from the host. 
The eggs are liberated and settle to the bottom of 
the stream, where they are eaten by small crustaceans, 
called cyclops, which in turn are eaten by small fish 
which form the food of the bass. 



494 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 




lodge in 
numarn. 
"muscles 
Causing 
trichinosis 



-worm is 
a Cjfs'Ls 
in iTiLcscle 
of pig 



ularly of children, do little or no harm. The Ascaris, a larger 
roundworm, sometimes infests children but is rarely dangerous to 
its host. 

The pork worm or trichina (trl-kl'na), however, is a parasite 

which may cause serious injury. It passes through the first 

,. r _~ part of its existence 

as a parasite in a 
pig or other verte- 
brate (cat, rat, or 
rabbit) ; it is en- 
closed in a tiny sac or 
cyst, in the muscles 
of its host. If un- 
dercooked pork con- 
taining these cysts is 
eaten by man, the 
covering is dissolved 
off by the action of 
the digestive fluids, 
and the living tri- 
china becomes free 
in the intestine of 
man. Here it repro- 
duces, and the young pass through the intestinal wall into muscles, 
causing inflammation there and resulting in a painful and often 
fatal disease known as trichinosis. The government at one time 
inspected pork for trichina, but since a microscopic examination of 
meat was necessary and it was impossible to examine all killed hogs 
in this way, the practice has been discontinued with the result that 
trichinosis is on the increase. All pork should be well cooked. 

Filaria are small roundworms that cause various tropical dis- 
eases — the most serious of which is elephantiasis. The parasites 
possibly enter the body in drinking water and some are probably 
introduced by the bite of a mosquito. 



imdar=- 
cookecC 
por-k is 

< the \v6rrn 
is freecC by 
dions-stive/ 
° juices 



yoxsng break" / 
ouft of Vn&jX 
iritest'inej 

of maix and 
migrate, 

In what way may poorly cooked pork be harmful to man ? 



Practical Exercise 23. Find out from local physicians if there has ever been 
a case of trichinosis in your community. If so, try to find out why it occurred. 
What kind of inspection of meats do you have in your community? 



THE HOOKWORM 



495 



/ 



the human 
. excretcc 
infects soil 



vorm enters 
skin from, 
dirt betveeii 
the. toes 



Demonstration 7. Use a microscopic slide to show hookworm. Why 
is it called " hookworm " ? 

The hookworm. The account of the discovery by Dr. C. W. 
Stiles of the Bureau of Animal Industry, that the laziness and shift- 
lessness of the " poor whites " of the South is partly due to a para- 
site called the hookworm, reads like a fairy tale. 

The people, largely farmers, become infected with a larval stage 
of the hookworm, which develops in moist earth. It enters the 
body usually through a break in the skin of the feet, for adults 
and children alike, in certain localities where the disease is com- 
mon, go barefoot to a considerable extent. 

A complicated journey from the skin to the intestine now follows. 
The larvae pass through the veins to the heart, from there to the 
lungs, where they bore into the air passages, and eventually reach 
the intestine by way 
of the throat. One 
result of the injury to 
the lungs is that many 
persons thus infected 
are subject to tuber- 
culosis. The adult 
hookworms, once in 
the food tube, fasten 
themselves to the 
walls which they 
puncture ; and then 
they feed upon the 
blood of their host. 
The loss of blood 
from this cause is 
not sufficient to ac- 
count for the blood- 

lessness of the person infected, but it has been discovered that the 
hookworm pours out into the wound a poison which prevents the 
blood from clotting rapidly ; hence a considerable loss of blood 
occurs from the wound after the hookworm has finished its meal 
and gone to another part of the intestine. 



fiora stomach 
to intestines 
hooKs oix-fe 
the"NVall 



\ 



is 

svttllovect 




Carried 
to heart 

\ 

to vessels 
in lungs 



breaks 
lttto the 
air -sacs 



up through 
Vmdpipe 
to the 
mouth 



Explain, from the diagram, how one may become infected 
with hookworm. 



496 MAN CONTBOLS HIS ENVIRONMENT FOlt HEALTH 

The prevention of bookworm lies in sanitary toilets and in 
proper covering for the feet. The remedy for the disease is very 
simple : thymol, which weakens the hold of the hookworm, fol- 
lowed by Epsom salts, which helps pass it from the body. 

For years a large area in the South undoubtedly has been 
retarded in its development by this parasite ; hundreds of millions 
of dollars have been wasted and thousands of lives have been 
needlessly sacrificed. The Rockefeller Foundation has made a 
study of conditions all over the world and finds that in almost all 
semitropical countries the hookworm is present and that in some 
parts of the world almost all the people are infected. 

" The hookworm is not a bit spectacular : it doesn't get itself discussed 
in legislative halls or furiously debated in political campaigns. Modest 
and unassuming, it does not aspire to such dignity. It is satisfied simply 
with (1) lowering the working efficiency and the pleasure of living in some- 
thing like two hundred thousand persons in Georgia and all other Southern 
states in proportion ; with (2) amassing a death rate higher than tubercu- 
losis, pneumonia, or typhoid fever ; with (3) stubbornly and quite effectu- 
ally retarding the agricultural and industrial development of the section ; 
with (4) nullifying the benefit of thousands of dollars spent upon educa- 
tion ; with (5) costing the South, in the course of a few decades, several 
hundred millions of dollars. More serious and closer at hand than the 
tariff ; . . . making the menace of the boll weevil laughable in compari- 
son — it is preeminently the problem of the South." — Atlanta Constitution. 

Practical Exercise 24. Work out a suggested control of hookworm in the 
United States and report to the class. 

Debate the statement from the Atlanta Constitution, using tuberculosis as 
the opposing disease. 

Self-Testing Exercise 

Check the true statements for your workbook : 

T. F. 1 . One form of tapeworm, parasitic in man, lives as an embryo in 
the muscles of cattle. 

T. F. 2. The tropical disease, elephantiasis, is caused by small round- 
worms. 

T. F. 3. People who live in hookworm-infested districts should 
never go barefoot. 



HOME CONDITIONS 



497 



The government examines all pork to see if it has trichina. 

Some tapeworms are given to pigs by man. 

Trichina is a roundworm that causes the disease called 

Hookworms are taken into the body by drinking impure 



T.F. 4. 

T.F. 5. 

T.F. 6. 
trichinosis. 

T.F. 7. 
water containing their eggs. 



PROBLEM XI. HOW MAY WE IMPROVE CONDITIONS AT 

HOME? 

The bedroom. Our work in general science has shown us the 
need of ventilation, especially in our bedrooms. The sleeping 
porch, so often found in country homes, is one of the most healthful 




Photo by Douglas — Xesmuth & Associates 
Why are these buildings poor examples of apartment houses ? 

of modern conveniences. Such a condition as this is manifestly 
impossible for most people in a crowded city. Until comparatively 
recent times, many tenement houses were built so that the bed- 
rooms had very little light or air ; but now, due to housing laws, 
wide airshafts and larger windows are required. Laws in some 



498 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

cities require that every room in a modern apartment, except the 
bathroom, must have at least ninety square feet of floor area, that 
every room must have one outside window, and that at least 
twenty per cent of a lot (except a corner lot) should not be built 
upon. 

In certain city tenements tuberculosis is believed to have been 
spread by people occupying rooms in which a previous tenant had 
tuberculosis. A new tenant should insist on a thorough cleaning 
of all the rooms and removal of old wall paper before occupancy. 

Practical Exercise 25. Why should we have rugs in our bedroom instead of 
carpets? How would you clean your bedroom? If you use the room for 
study as well as sleeping, draw a plan for the arrangement of furniture and 
give reasons for its disposal. Show how you would get the best ventilatior 
for sleeping. 

Sunlight is of great importance to health. Every home should 
have sunlight for a part of the day at least in its living and sleeping 
rooms. Sunlight is still the greatest germicide we know. 

A student lamp, or shaded incandescent light, should be used 
for reading, so that the eyes are protected from direct light. Gas 
is a dangerous servant, because it contains carbon monoxide. 
It has been estimated that fourteen per cent of the total product 
of the gas plant leaks into the streets and houses of the cities sup- 
plied. This forms an unseen menace to health in cities. 

Practical Exercise 26. Contrast indirect- and direct-lighting systems in 
your home from the standpoint of efficiency and protection of your eyes. 

Care of food in the home. Although we can buy many foods 
in sealed packages, much of our food is exposed to the handling of 
people who may be careless. Vegetables and meats are too often 
exposed to dust, dirt, and handling. Raw fruits and vegetables 
should be carefully washed before being eaten. 

In the summer, our houses should be provided with screens. All 
food should be carefully protected from flies. Dirty dishes, scraps 
of food, and garbage should be quickly cleaned up and disposed of 
after a meal. 

Carelessness in dishwashing may mean the spreading of disease. 
Dr. Broadhurst of Teachers College, New York, learned, through a 
series of tests with several hundred glasses and cups smeared with 



CARE OF FOOD IN THE HOME 



499 



saliva, that when dishes are hand washed and not rinsed all the 
bacteria are not removed. Some of the bacteria are not destroyed 
unless boiling hot water is used. At the time of the influenza 
epidemic during the World War an investigation was made of 
66,000 men, half of whom ate 



cases of influenza 
and. dish"washing 



£1 per 1000 

-when dishes 
are v/asYiedi 
in boiling 
hot -water* 



252 per 1000 

-when dishes 
cere, not^ 

^cts-teed 



Explain, from text, what this diagram means. 



from plates which were washed 

in boiling water, the other half 

from mess plates which were 

washed carelessly by the men. 

The influenza rate was 51 per 

1000 among the men who ate 

from properly washed dishes, 

and 252 per 1000 among the 

men who ate from mess plates. These facts show plainly the 

need of proper washing of dishes. 

Milk at home should receive the best of care. It should be kept 
on ice and in covered bottles, because it readily takes up the 
odors of other foods. If we are not certain of its purity or keeping 
qualities, it should be pasteurized at home. Why? Experiments 
made with good fresh milk, which at the first observation contained 
about 30,000 bacteria per cubic centimeter, showed that twenty- 
four hours later, if kept at the temperature of the average ice box 
(below 50° Fahrenheit), there were about the same number of 
bacteria present; while some of the same milk exposed to a 
temperature of 68° Fahrenheit showed 500,000,000 bacteria to the 
cubic centimeter. 

Demonstration 8. To determine the bacterial content of milk of 
various grades and from different sources. 

Put a couple of drops of certified, pasteurized, raw, etc., milk, in 
separate Petri dishes containing sterile agar. Cover the dishes and 
put them in a warm dark place (about 90° F.) for 24 hours. Which 
dish shows the greatest number of colonies? The greatest number of 
different colonies? Which is the best kind of milk to use ? Why? 

Demonstration 9. To determine the bacterial content of distilled 
water, rain water, tap water, dilute sewage. 

Put several drops of the various kinds of water on dishes containing 
sterile agar. Cover the dishes and put them in a warm dark place for 
24 hours. Which dish contains the greatest number of colonies? The 
greatest number of different colonies? Which is the best water to use for 
drinking purposes? For cooking? For laundry? Why? 



500 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

Practical Exercise 27. What general facts have you learned about refriger- 
ation ? What types of refrigerators are most efficient ? The most costly to pur- 
chase ? The most costly to run ? What recommendation would you make for 
the average small family living in the country? In the city? 

Practical Exercise 28. What insects are household pests ? Which of these 
damage foods? What would you do to rid a house of ants? Roaches? 

Practical Exercise 29. Is cold-storage food as good as fresh food? Give 
reasons for your answer. Recent tests have shown that the majority of cheap 
ice boxes do not keep the temperature below 50° F. Such boxes usually have 
the ice wrapped in newspapers when it is put in the box. What effect does 
the paper have on the efficiency of the ice box? 

Home water supplies. We have already learned why water 
which comes from a shallow well or unprotected spring should be 
carefully tested and protected against pollution. Ice for use 
in drinking water should be carefully washed, for experiments 
show that although nearly all bacteria in ice are killed after storage 
of a few weeks, yet disease germs are often found on the outside of 
pieces of ice because it is handled by disease carriers or persons of 
careless personal habits. Water coolers and filters are usually 
traps for bacteria and are often dangers rather than aids in sani- 
tary living. Moreover, a water cooler in a house is frequently ac- 
companied by a common drinking cup. 

Practical Exercise 30. Show what you would do to protect a home water 
supply of uncertain purity. Make a report to the class. 

Disposal of wastes. In country homes where cesspools receive 
human wastes, great care should be used in locating them, espe- 
cially if the water supply is from a shallow well. A septic tank 
costs little more to install and is much safer than the ordinary 
cesspool. In city houses the disposal of human wastes is pro- 
vided for by a system of sewers. Garbage should be disposed 
of each day. The garbage pail should be frequently sterilized by 
rinsing it with boiling water and plenty of lye or soap. Remember 
that flies frequent the uncovered garbage pail, and that they fly 
from it to your food. 

Practical Exercise 31. Make a diagram for your workbook to show the 
method of sewage disposal in your community; in your home. 

Find out the method of garbage collection and disposal in your town. 
Make suggestions for improvement of this service, if needed. 



SCHOOL SURROUNDINGS 501 

Self-Testing Exercise 

The best known germicide is (1). Some cities require 

the rooms of all apartments to have (2) (3). Gas 

leaks are harmful because of the danger of (4) (5) . 

Bacteria on dishes can only be destroyed by (6) (7). 

Foods should be protected from (8). Milk in home should 

be kept on (9) to prevent (10) of (11). 

Water supplies should be (12) and (13) against 

pollution. A septic tank is (14) than a (15). 



PROBLEM XH. HOW MAY WE IMPROVE CONDITIONS AT 
SCHOOL? 

School surroundings. For forty weeks in the year from five to 
six hours a day are spent by the average boy or girl in the schoolroom. 
It is part of our environment and should therefore be considered 
as worthy of our care. A schoolroom should be not only attractive, 
but also clean and sanitary. City schools, because of their loca- 
tion, poor janitor service, or the selfishness and carelessness of chil- 
dren who use them, may be very dirty and unsanitary. Bacteria 
thrive in warm moist places where food is present, and float in the 
air with particles of dust. Experiments show that there are many 
more bacteria in the air when pupils are moving about, for then 
dust, bearing bacteria, is stirred up and circulated through the 
air. Sweeping and dusting with dry brooms or dusters stirs up 
the dust, which settles in some other place with its load of bacteria. 
Professor Hodge tells of an experience in a school in Worcester, 
Massachusetts. A health brigade was formed among the children, 
whose duty was to clean the rooms every morning by wiping all 
exposed surfaces with damp cloths. In a school of 425 pupils not 
a single case of communicable disease appeared during the entire 
year. Hundreds of schools have tried experiments similar to this 
and always with the same result, a pleasanter and cleaner building 
and better health of pupils. 

Pupils should be unselfish in the care of a school building. 
Papers and scraps dropped by some careless boy or girl make the 
surroundings unpleasant for hundreds of others. Chalk thrown 
h. bio — 33 



502 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

by some mischievous boy and then tramped under foot causes 
dust particles in the air, which may irritate the lungs of a hundred 
schoolmates. Colds may be spread by spitting in the halls or on the 
stairways. Do not be the one to do such an unsportsmanlike act. 




Keystone View Co. 



Why might this be considered an ideal high school building ? 

Project. To form a service squad in your school. Make a report 
on such school conditions as may be remedied by concerted or indi- 
vidual student action and present it to the class. If conditions 
warrant it, ask your principal to hold a clean-up week, have a health 
assembly, or in some other way start public sentiment in the school 
for better cooperation and a more sanitary school plant. 

Demonstration 10. To show the effect of the use of a duster and 
of a damp cloth upon bacteria in the schoolroom. 

Expose a dish of sterile agar for a few minutes in a room which is 
being dusted with a dry cloth or feather duster. Expose another dish 
of sterile agar in a room which is being dusted with a damp cloth. Cover 
the two dishes and keep them in a warm place for 24 hours. What is 
the result ? 



Lunch time and lunches. Lunches should be clean, tasty, and 
well balanced. In most large schools, lunch rooms are part of the 
equipment and balanced lunches can be obtained at low cost. 
Do not make a lunch entirely from cold food, when hot can be 



INSPECTION OF FACTORIES 503 

obtained. Do not eat sweets only. Ice cream is a good food, if 
taken with something else, but be sure of the quality of your ice 
cream. More than 250 samples of ice cream collected and exam- 
ined in Washington, D. C, contained from 37,500 to 365,000,000 
bacteria per cubic centimeter. The condition of ice cream de- 
pends largely on the sanitary conditions of the place where it was 
manufactured. Above all, be sure that all the food you eat is clean. 
Stands on the street, exposed to dust and germs, often have for 
sale food that is far from fit for human consumption. If you 
eat your lunch on the street near your school, remember not to 
scatter refuse. Paper, bits of lunch, and the like, scattered on 
the streets around your school, show lack of school spirit and 
lack of civic pride. 

Project. Get help from your teacher or the local board of health 
in testing the purity of ice cream and other foods sold from stands 
outside the school. Test foods in your own school cafeteria at the 
same time as a control to see which conditions are better. 

Self-Testing Exercise 

Check the correct statements for your workbook : 

T. F. 1. Schools are often dusty because of the movement of chil- 
dren through the halls. 

T. F. 2. Feather dusters are better than wet cloths because the 
cloths stain the woodwork. 

T. F. 3. Luncheons should be tasty as well as clean and well-balanced. 

T. F. 4. Ice cream is always a safe food because freezing kills 
bacteria. 

T. F. 5. If foods are exposed, the sunlight will kill the bacteria. 

PROBLEM XIII. HOW MAY WE HELP IMPROVE CONDITIONS 
IN OUR COMMUNITY? 

Inspection of factories and public buildings. It is the duty of a 
city to inspect the condition of all public buildings, especially of 
factories. Certain trades where dirt or poisonous fumes are given 
off are dangerous to health, hence care for the workers becomes 
a necessity. In such places the machinery must be protected 
by hoods or ventilators to carry off the fumes, and the workmen 
must be provided with dust and fume masks. Often goggles are 
provided to protect the eyes from dust or bright light. There 



504 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

are other occupations where noise, monotony of work, or too rapid 
movement causes fatigue and frequently accidents. Workmen in 
such trades must be protected, and many state laws now provide for 
proper gas masks, wheel and belt protectors, efficient lighting and 

other devices that 
protect workmen 
from the particu- 
lar hazard to which 
they are exposed. 
Factories are in- 
spected as to clean- 
liness, the amount 
of air space per 
person employed, 
ventilation, toilet 
facilities, and 
proper fire protec- 
tion. Tenement 
inspection should 
also be thorough 
and should aim to 
provide safe and 
sanitary homes for 
workers and their 
families. 

Inspection of food supplies. In all cities certain regulations for 
the care of public food supplies are necessary. Inspectors are 
appointed to see that the laws are enforced and that foods are pro- 
tected for the thousands of people who are to use them. All raw 
foods on stands should be covered with glass so as to prevent in- 
sects or dust laden with bacteria from coming in contact with them. 
Meats must be inspected for diseases. Inspection of cold-storage 
plants, of factories where foods are canned, and of bakeries must 
be and is part of the work of a city in caring for its citizens. 




Why is the face of this workman protected with a shield ? 



Practical Exercise 32. Visit a factory in your neighborhood and report to 
the class on all the protection devices you found. Have you any suggestions 
for improvement ? 



SEWAGE DISPOSAL 



505 



Project. Inspect the conditions in your own home block or in the 
town in which you live. Make a map showing the buildings. Locate 
all houses, stores, factories, etc. Indicate any cases of communicable 
disease on the map. Mark all heaps of refuse in the street, all un- 
covered garbage pails, any street stands or push carts which sell 
uncovered fruit, and any 
stores which have an ex- 
cessive number of flies. 
Note any other unsanitary 
conditions and mark them 
with appropriate symbols. 

Sewage disposal. Sew- 
age disposal is an impor- 
tant sanitary problem for 
every city. Some cities, 
like New York, pour their 
sewage directly into rivers 
which flow into the ocean. 
Consequently, much of 
the liquid which bathes 
the shores of Manhattan 
Island is dilute sewage. 
Other cities, like Buffalo 
or Cleveland, send their 
sewage into the lakes from 
which they obtain their 
supply of drinking water. 
The city of Chicago has 

built a huge drainage canal which diverts water from Lake Michi- 
gan. Through this canal the sewage is diluted and is carried 
eventually into the Mississippi River by way of the Illinois River. 
While there is not a noticeable increase in the bacterial content of 
the Illinois River at the point where it flows into the Mississippi, 
this drainage canal has done harm in another way. The fish in the 
upper Illinois River have been driven out or killed by the factory 
refuse and other wastes which come down the canal. This is only 
one example of the pollution of rivers by sewage and especially by 
factory wastes. All over the eastern part of our country rivers 
have been made open sewers, and now the conservation of our fish, 




Armour and Co. 

Inspectors are employed by the government to inspect 
and stamp all meat sent to other states. 



506 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



as well as the water supply of many of our cities, is becoming a 
serious problem. 

The best way to avoid the pollution of rivers is by proper sewage 
disposal, even if this method is expensive. Sewers for large cities 
are planned so that the dilute sewage is carried to a sewage dis- 
posal plant, usually situated a short distance outside of the com- 
munity. Here the solid wastes are screened out, and then the 
smaller particles are precipitated out. The disposal of the solid 
material, called sludge, is still a serious problem. In some cities 
this sludge is dried, treated, and used as fertilizer. The fluid 
sewage, after the solid matter is taken out, is usually run over 
filter beds composed of coarse sand. In these filters bacteria 
oxidize the remaining organic matter of the sewage, so that the 
liquid which flows off is harmless and odorless. But such water 
is never used until it is first treated with chemicals, such as 
chlorine, in order to kill any harmful germs that may be left. 

Practical Exercise 33. Report on an up-to-date method of sewage disposal 
in some city or community. Compare the conditions of this city with those 
existing in your community. 

The work of the department of street cleaning. Another city 
problem is the disposal of refuse and garbage. The city streets, 





Culture A was exposed to the air in a well-cleaned and watered street in a residential 
section of a city. Culture B was exposed to the air in a crowded street in a business section 
of the same city. How do you account for the differences and results ? 

when dirty, contain countless millions of germs which have come 
from decaying material or from people and animals more or less 



DEPARTMENT OF STREET CLEANING 507 

diseased. In most large cities a department of street cleaning not 
only cares for the removal of dust from the streets, but also has the 
removal of garbage, ashes, and other waste as a part of its work. 
The disposal of solid wastes is a tremendous task. In Manhattan, 
New York, the dry wastes are estimated to be 1,000,000 tons a year 
in addition to about 175,000 tons of garbage. In some cities, such 
as Minneapolis, garbage must be wrapped in paper. This aids 
burning it in the city incinerator. In many cities the garbage is 
removed in carts, and part of it is burned in huge furnaces. The 
animal and plant refuse are sometimes cooked in great tanks, the 
fats extracted from this material, and the solid matter sold for 
fertilizer. Ashes are used in some places for filling marsh land. 
Thus the removal of waste matter may pay for itself in a large 
city. 

Practical Exercise 34. Report to the class on the conditions existing in your 
community with reference to disposal of garbage, ashes, and other wastes. 
What rules exist? Is the collection of garbage and ashes a city or private 
function? What is done with reference to street cleaning? 

Self-Testing Exercise 

Check the correct statements for your workbook : 

T. F. 1. Some occupations, such as trades which have dust or 
poisonous fumes, are dangerous. 

T. F. 2. Food supplies which are not packed in containers do not 
need to be inspected. 

T. F. 3. The government inspects all food so there is no danger 
to the consumer. 

T. F. 4. People could safely drink dilute sewage if it were first 
filtered and chlorinated. 

T. F. 5. Pollution of our streams with sewage not only drives out 
or kills the fish but makes the polluted stream a menace to health. 

T. F. 6. The best method of sewage disposal for large cities is 
treating it with chemicals. 

PROBLEM XIV. WHAT PROTECTIVE HEALTH AGENCIES 
SHOULD EXIST IN A COMMUNITY? 

Practical Exercise 35. Compare the functions of your local board of health 
with those listed in the diagram on page 508. How many departments, if 
any, has it? How large a community does it serve? How many board mem- 
bers are there ? Are they paid or volunteer workers ? What work do they do ? 



508 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



Are there any laboratories ? If so, describe them. Do the local health officers 
concur with all the activities shown on the diagram? To what extent? 

Has your locality an efficient board of health? If not, what suggestion 
can you make for improvement? 

Public hygiene. Although it is absolutely necessary for each 
individual to obey the laws of health in order to keep well, it has 
become necessary also, especially in large cities, to have a depart- 
ment or board of health to exercise general supervision over the 
health of the people living in the community. In addition to such a 
body in cities, supervision over the health of citizens is also exercised 
by state boards of health. Since 1912 the United States Public 
Health Service has had general supervision over interstate quaran- 
tine and public health. Its valuable reports and reprints are avail- 
able for schools and should be used in your project and classwork. 

The functions of a city board of health. The administration 
of the board of health of a city includes a number of divisions, 

each one of which 



sanitation 



fooct 
Supplies 



child 
hygiene 




laboratories 



divisions' of the 

HEALTH 
DEPAT5T7v\ENT 



publicity and 
education. 



vital 
statistics 



tuberculosis 



communicable 
diseases 



has a different work 
to do. Each is in it- 
self important, and, 
working together, 
the entire machine 
provides ways and 
means for making a 
great city a safe and 
sanitary place in 
which to live. A 
local health board, 
according to an au- 
thority, Dr. C. E. A. Winslow, should supervise the food supplies and 
sanitation of a city. It should from its laboratories take care of the 
communicable diseases by means of vaccines and antitoxins. It 
should have a department of child hygiene and should carry on 
health campaigns through its department of publicity and educa- 
tion. Finally, it should publish the vital statistics of the community. 
The division of communicable diseases. Communicable dis- 
eases are chiefly spread through personal contact. It is the duty 
of a government to prevent a person having such a disease from 



The health departments of various cities ; counties, or states 
have a number of divisions. How many are there in your city 
and state departments of health ? 



THE DIVISION OF COMMUNICABLE DISEASES 509 

spreading it among his neighbors. This is done by the board of 
health requiring the quarantine or the isolation of the person 




Nat. T. B. Assn. 

Some health agencies, schools, and sanitariums provide camps for children who are under- 
nourished or who have been in direct contact with persons suffering from tuberculosis. 

having the disease. No one save the doctor and the nurse should 
enter the room of the person quarantined. After the disease has 
run its course, the clothing, bedding, etc., in the sick room are dis- 
infected. This is known as terminal disinfection. 

Tuberculosis, which not many years ago killed fully one seventh 
of the people who died from disease in this country, now kills less 
than one tenth. This decrease has been brought about largely 
through the treatment of the disease. Since it has been proved 
that tuberculosis, if treated early enough, is cured by quiet living, 
good food, and plenty of fresh air and light, we find that numerous 
sanitariums have come into existence which are supported by 
private or public means. At these sanitariums the patients live 
out of doors, and sleep in the open air, and have plenty of nourish- 



510 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

ing food and little exercise. Hundreds of sanitariums are now 
established in various parts of the country and are maintained by 
taxation as a part of the expenditure of the city, county, and state 
boards of health. There are many private sanitariums as well, 
maintained by various benevolent orders. In this way and by 
laws which require proper air shafts and window ventilation in 
tenement houses, by laws against spitting in public places, and in 
other ways, the boards of health in our towns and cities are waging 
war on tuberculosis. 

Work of the division of school and infant hygiene. Besides 
the division of communicable diseases, the division of sanitation, 
which regulates the general sanitary conditions of houses and their 
surroundings, and the division of inspection, which looks after the 
purity and conditions of sale and delivery of milk and foods, there 
is another division which most vitally concerns school children. 
This is the division of school and infant hygiene, which supervises 
the care of the children of the city. 

Adenoids. Many children suffer needlessly from enlarged 
tonsils and adenoids — growths in the back of the nose and mouth 
which cut off part of the normal supply of air to the lungs. A child 
suffering from these growths is usually a " mouth breather." The 
result to the child may be deafness, chronic running of the nose, 
nervousness, and lack of power to think. His body cells are 
starving for oxygen. A very simple operation removes these 
growths. Cooperation of the children and parents with the doc- 
tors or nurses of the board of health will do much in removing this 
handicap from many young lives. 

Eyestrain. Another handicap to a boy or a girl is eyestrain. 
In a survey, sometime ago, twenty-two per cent of the school chil- 
dren of Massachusetts were found to have defects in vision. Tests 
for defective eyesight may be made easily at school by competent 
doctors, and if the weakness is corrected by procuring proper 
glasses, a handicap on future success will be removed. 

Physical examinations. Decayed teeth are another handicap 
cared for by this division. Free dental clinics have been established 
in many cities, and if children will do their share in caring for their 
teeth, the chances of their success in later life will be greatly aided. 



PHYSICAL EXAMINATIONS 511 

In the schools of Elizabeth, N. J., in 1925 there were nearly 13,000 
children examined for physical defects. These were placed in 
four groups, depending on the condition of physical well-being. 
Here the group that was in best health showed the best school 
grades, while those in poorest health had the poorest grades. Boys 
and girls, if handicapped with poor eyes or teeth, do not have a 
fair chance in life's competition. In a certain school in New York 
there were 236 pupils marked " C " in their school work. These 
children were examined, and 126 were found to have bad teeth, 
54 to have defective vision, and 56 to have other defects, as poor 
hearing, adenoids, enlarged tonsils, etc. Of these children, 185 
were treated for these various difficulties, and 51 did not take 
treatment. During the following year's work 176 of these pupils 
improved from " C " to " B " or " A," while 60 did not improve. 
If defects are such a handicap in school, what will be their effect 
on the chances of success in life outside ? 

The department of school hygiene deserves the earnest coopera- 
tion of every young citizen, girl or boy. If each of us would 
honestly help by maintaining quarantine in the case of communi- 
cable disease, by observing the rules of the health department, by 
acting upon reliable advice in case of eyestrain, bad teeth, or 
adenoids, and most of all by observing the rules of personal hygiene, 
the community in which we live, a generation hence, would be com- 
posed of stronger, more prosperous, and more efficient citizens. 

Practical Exercise 36. Make an outline of all the health-protective agencies 
in your community. 

Practical Exercise 37. Tell what is being done in your own school to check 
on the health of the students. Is there any " follow up " of those who are 
not well? 

Self-Testing Exercise 

Check the correct statements for your workbook : 

T. F. 1. The function of the U. S. Public Health Service is to 
control my city health department. 

T. F. 2. Quarantine is a protective measure and should be obeyed. 

T. F. 3. Tuberculosis can be controlled entirely through sani- 
tariums. 

T. F. 4. Children whose health is poor usually have poor school 
grades. 



512 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

Review Summary 

Test your knowledge of the unit by: (1) rechecking on the survey ques- 
tions ; (2) performing the assigned exercises ; (3) checking with your teacher 
your scores on the various tests and doing over those that you missed ; (4) mak- 
ing an outline of the unit for your work book. 

Test on Fundamental Concepts 

In a vertical column under the heading CORRECT write numbers of all statements you be- 
lieve are true. In another column under INCORRECT write numbers of untrue statements. 
Your grade = right answers X 2. 

I. Quarantine (1) is necessary because it gives the patient a rest; 
(2) is necessary because by isolating a person sick with a disease we may 
keep others from having it; (3) is useless except in early stages of 
disease ; (4) is an unselfish action because it protects others ; (5) should 
be enforced on all persons who have had contact with a person ill 
with communicable disease until the incubation period of that disease 
has been passed. 

II. Immunity (6) means that a person can never take a certain 
disease, no matter if he is exposed to it ; (7) is always specific, that is, 
against one disease (A person may be immune to smallpox and be 
susceptible to measles) ; (8) is never restricted to certain races, whites 
and Negroes being equally susceptible to tuberculosis ; (9) is natural 
to some people but not to others; (10) is not modified by a person's 
condition. 

III. Active immunity (11) is gained by means of antitoxins; 
(12) takes place when the body helps to fight the disease by making 
antibodies in the blood ; (13) is brought about against smallpox through 
vaccination ; (14) is gained in typhoid through the introduction of dead 
germs with their toxins ; (15) is not possible unless the blood makes 
antibodies. 

IV. Passive immunity (16) occurs when the body fights the disease 
by making its own antitoxins; (17) is seen in the antitoxin treatment 
against diphtheria ; (18) is brought about when an antitoxin is formed 
outside the body and is injected into the body to help fight the disease ; 
(19) is shown by Schick test and Dick test ; (20) is not useful, for sta- 
tistics show it has not reduced the death rate in diphtheria. 

V. The way to keep well (21) is to have immunity against all the 
diseases given at once and get it over with ; (22) is to keep the body 



ACHIEVEMENT TEST 513 

resistance high through sensible living ; (23) is to avoid people whom 
you think have communicable diseases; (24) is to have plenty of 
nourishing food at regular times, plenty of sleep, and work and play 
in moderation ; (25) is never to worry, and to take proper precautions 
in case of illness of others. 

VI. Animals (26) may cause disease, as the malarial parasite; 
(27) may cause disease, as the Culex mosquito; (28) may spread 
disease, as the house fly ; (29) may be parasites in two different hosts, 
needing both to complete their life cycle ; (30) are only harmful if 
they are parasites. 

VII. Malaria (31) may be controlled by killing off the Anopheles 
mosquito; (32) is only known in the tropics; (33) is caused by 
mosquitoes ; (34) may be cured by taking quinine ; (35) is caused by a 
protozoan. 

VIII. The following animals may act as carriers of human disease : 

(36) rats; (37) birds; (38) pigs; (39) flies; (40) fleas. 

IX. We may improve conditions in our community (41) by 
always voting for all public measures without investigating their 
value because those who make the laws know best ; (42) by making 
sure that our public water supply is protected by chlorination and 
filtration if the source is not pure ; (43) by insisting upon pure milk 
and regulations that provide for it; (44) by patronizing all stores 
equally, clean and dirty ones; (45) by cooperation with the health 
department. 

X. The protective health agencies of much value in a community 

are (46) the city council; (47) the board of aldermen; (48) the 
board of health; (49) hospitals and sanitariums; (50) the division 
of school health and hygiene. 

Achievement Test 

1. How have you cooperated with the health authorities in the 
matter of quarantine after exposure to a communicable disease? 

2. What is the value of acquired immunity? 

3. What is the story of malaria in Microbe Hunters? 

4. What is the story of yellow fever in either Microbe Hunters or 
Health Heroes? 

5: How may malaria and yellow fever be controlled ? 
6. How may we get rid of flies ? 



514 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

7. What are all the insects that spread diseases ? Suggest a way 
to control them. 

8. Have you made a fly and mosquito survey of your neighbor- 
hood? What did you find? 

9. Have you made a survey of your home and surroundings and 
estimated the yearly damage done to them by rats ? What is it ? 

10. What do the reports of the Rockefeller Foundation say about 
the extent hookworm has been controlled ? 

11. How do the various unfavorable factors of your environment 
affect your home and how may you prevent such factors from doing 
harm? 

12. Have you a service squad in your school? What do you do 
to make its work effective ? 

13. What facts do you know about sewage and garbage disposal 
in your community? 

14. How is the health department of your community organized 
and how does it do its work? 



Practical Problems 

1. Describe the process of making vaccines. Ask your teacher 
for references. 

2. Suppose your city was threatened with a typhoid epidemic. 
Outline the probable procedure of the Board of Health and list your 
part in fighting the epidemic. 

3. Suppose your home was made uncomfortable from mosquitoes 
coming from an unknown source. The rest of the community is 
not bothered by them. Outline your procedure in ridding your home 
of these pests. 

4. What do you know of the sanitary conditions of your own 
home ? Can you locate sewers, cesspool, or septic tanks, etc. ? Do 
you know if your water supply is tested regularly and is adequately 
protected? Do you have regular garbage collection? Do you know 
how garbage is disposed of? How is the food in your home protected? 
Are you properly screened against insects? How high a score would 
you and your home make on the following score card ? 

a. Environment 

Pure air 10 

Pure water 10 

Well-drained soil 10 

Plenty of sunlight 10 

Not too great extreme of heat or cold 5 

Foods supplied from home garden 5 

Foods cheap and good 5 



PRACTICAL PROBLEMS 515 

h. Water in my home 

Safe supply 10 

Ample supply 10 

All parts of home supplied 10 

Plumbing in good condition 10 

Soft water provided 10 

c. Care of foods in my home 

Clean kitchen and utensils 10 

Good refrigeration 10 

Sterilization and pasteurization 10 

Proper use of preservatives 10 

Protection from insects, etc 10 

d. Household pests 

No flies 10 

No mosquitoes 10 

No body pests (fleas, bedbugs, head lice) 10 

No food or cloth pests (roaches, ants, weevils, clothes moths, etc.) 10 

No rats or mice 10 

e. Removal of wastes 

Exposed plumbing 10 

All porcelain fixtures 10 

Have a working knowledge of system 10 

Sewer connections or septic tank 10 

Garbage pail properly kept 10 

/. Personal health habits 

Setting-up drill and deep breathing 5 

Cool rub or shower every day 5 

Teeth brushed morning and night 5 

Slow eating at meals 5 

Food chewed well . 5 

No overeating 5 

Cheerfulness at meals 5 

Regular toilet habits 5 

Wash hands often 5 

Clean shoes and clean linen . . 5 

Loose, comfortable clothing 5 

Feet warm and dry 5 

Regular play hours 5 

Exercise in open air two hours a day 5 

Regular work and study hours (at least two hours) 5 

Proper lighting for study '5 

Bed before 10 p.m 5 

Sleep in open air or with windows open top and bottom 5 

No coffee, tea, or cigarettes 5 

g. Protection against disease 

Vaccinated for smallpox 5 

Teeth examined twice a year 5 

All teeth cavities filled 5 

Eyes examined once a year 5 

Glasses used when necessary 5 



516 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 

Keep more than five feet distant from those who cough or sneeze . 5 

Take care to use handkerchief if you cough or sneeze 5 

Stay in the house if you have a cold 5 

All clothing clean and sterile at all times 5 

Wounds properly disinfected 5 

h. Clothing, bathing, and ventilation 

Proper outer clothing 10 

Proper and clean underclothing 10 

Bathing twice a week at least 10 

Proper bedroom hygiene 10 

Proper home ventilation 10 

i. Lighting my home 

Sunlight plentiful 10 

Windows ample, wall papers good reflectors 10 

Artificial light economical 10 

Proper lighting for all kinds of work 10 

Good systems of lighting used _10 

Total Possible Score 500 

5. What do you know about the sanitation of your own com- 
munity? Its water supplies, milk and food inspection, garbage and 
ash disposal, sewage disposal? What agencies care for each of the 
above? What would you do in case of a typhoid outbreak in your 
city? Septic sore throat? Tuberculosis of children? 

6. Is your school adequately ventilated? Is its heating plant, 
the sanitary condition of its toilets, gymnasium, and the methods of 
cleaning the best possible? 

7. What is the Board of Education doing to protect your health? 

8. Do you have a sanitary code in your community? If so, who 
administers it? What do you know about it? Is there adequate 
inspection of food supplies? Care of milk? Do you know where 
the milk you drink comes from and how it is cared for ? 

9. To what extent in the past have you, as a young citizen, 
cooperated with the authorities to make your town a more sanitary 
and safer place to live in? 

Useful References 

Allen, Civics and Health. (Ginn & Co.) 

Andress, Aldinger, Goldberger, Health Essentials. (Ginn & Co. 1928.) 

Broadhurst, Home and Community Hygiene. (J. B. Lippincott Co. 

1925.) 
Broadhurst, How We Resist Diseases. (J. B. Lippincott Co. 1923.) 
Bulletins and Publications of Committee of One Hundred on National 

Health. 
De Kruif, Microbe Hunters. (Harcourt, Brace & Co. 1926.) 
Farmers' Bulletins : 70, 658, 851. 
Hunter, Laboratory Problems in Civic Biology. (American Book 

Company.) 



USEFUL REFERENCES 517 

Hygeia. (American Medical Association.) 

Jewett, Town and City. (Ginn & Co.) 

Public Health Reprints : 54, 78, 106, 192, 234, 302, 341, 441, 448, 499, 

530, 680, 723, 821, 827, 850. 
Reports of Boards of Health of California, Illinois, New York, Virginia, 

etc. ; and of the City of New York and other cities. 
Richards, Sanitation in Daily Life. (M. Barrows & Co.) 
Richman and Wallach, Good Citizenship. (American Book Company.) 
Ritchie, Primer of Sanitation. (World Book Co. 1925.) 
School Hygiene. (American School Hygiene Association.) 
Sharp, Foundation of Health. (Lea & Febiger. 1924.) 
Tolman, Hygiene for the Worker. (American Book Company.) 
Winslow, Healthy Living. (Charles E. Merrill Co. 1920.) 
Zinsser, Textbook of Bacteriology. (D. Appleton & Co. 1927.) 



H. BIO — 34 




SURVEY QUESTIONS 

What do we mean by economic value ? What plants have the greatest 
economic value in your locality ? Why are birds called the farmer's best 
friends ? How can you conserve bird life in your community ? What crops 
are damaged by insects ? How are insect pests controlled ? 



Ewing Galloway 



UNIT XVI 



HOW DOES MAN CONTROL HIS ENVIRONMENT FOR 

WEALTH? 

Preview. To the boy or the girl living in the city green plants 
seem to have little direct value. Although we see vegetables for 
sale in stores, and we know that fruits have a money value, we are 
not likely to realize that the wealth of our nations depends upon 
growing crops more than it does on manufactories and business 
houses. The economic or " dollars and cents " value of plants is 
enormous, and our lives depend on the food which they supply. 

Another great source of wealth is the animals man uses for food, 
as a source of raw material for clothing, furs, dyes, oils, perfumes, 

518 



PREVIEW 519 

and many other commodities. But both plants and animals have, 
in another sense from the above, an economic value. If plants, 
such as weeds, destroy our crops by taking their place, or if animals, 
such as coyotes, destroy sheep by killing them, then they are harm- 
ful in a " dollars and cents " way. 

We have already learned that man plays a very important part 
in disturbing the balance of life as it exists on the earth. This has 
been brought about by the increased population and the conse- 
quent necessary increase in food and other supplies. Through 
planting crops which have nitrogen-fixing bacteria associated with 
them, it has become possible for the earth to supply more crops. 
By irrigating large areas of practically desert land man has been 
able to raise large crops of grains, vegetables, and fruits. 

Man is also constantly finding new uses for animal products. 
Fishes, such as the dogfish, which were formerly unmarketable, 
because they were not thought good to eat, are now an article of 
food under the name of the grayfish. This is only one instance of 
how man, as the thinking animal, exploits other forms for his own 
benefit. More people on the earth means a need for more food. 
Man has come to realize the way in which he has been wasting the 
living things which he needs and he is emphasizing methods of 
conservation as well as the use for food of plants and animals that 
formerly were not considered as fit for food. 

Those of us who live in farming communities are aware of the 
harm done by many insects and know, too, that our bird friends do 
a good deal to help make it possible for the farmer to raise his crops. 
But those of us who do not know the birds as friendly fighters in 
our behalf should have some evidence along this line. Moreover, 
all of us ought to know a few common birds so we may be able to 
recognize them. 

Birds not only eat insects but some of them eat weed seeds, thus 
keeping these pests somewhat more under control. Even the 
birds which do eat crops make up for this by feeding in part upon 
insects or harmful rodents. 

To understand the value of birds better a few examples of in- 
sect damage will be given and, when possible, it will be shown 
how insects are controlled by the birds which feed upon them. 



520 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

PROBLEM I. HOW ARE PLANTS USED AS FOOD? 

Leaves as food. Grazing animals feed almost entirely on tender 
shoots, leaves, or blades of grass. We can realize the economic 
value of grass when we consider the fact that for the last ten years 
the hay crop in this country was worth well over $1,000,000,000 a 
year. And this does not take into account the wild grasses used 
as forage by numerous grazing animals. 

Certain leaves and buds are used as food by man. Lettuce, 
kale, spinach, and broccoli are examples. A cabbage head is a 




What vegetables are leaves? Do you know any others? 



Wright Pierce 



large leaf bud. An onion is a compact budlike mass of thickened 
leaves which contain stored food. 

Practical Exercise 1. Make a table of foods to be filled out from material 
found in this unit and in books of reference. Fill out the first column of this 
table by placing in it ten leaves used as food by man. 

FOOD OF MAN 



Leaves 


Stems 


Roots 


Seeds 


Flowers 


Fruits . 















Stems as food. If one were asked to name a stem used as food, 
he would probably mention either asparagus or celery. Sugar 



STEMS AS FOOD 



521 




Wright Pierce 
Can you name stems, other than those given above, that are used for food ? 

cane certainly ought to be named also, since over half of the 
world's supply of sugar comes from this source. Maple sugar is a 
much used commodity obtained from the sap drawn from the 
trunks (enlarged stems) of sugar maples. Over 16,000 tons of this 
sugar is produced every spring. The pithy stem or trunk of the 
sago palm, grown by the native of the East Indies, is made into a 
meal or flour. This flour is shipped to all parts of the world and 
is used for making starch, puddings, and for thickening soups. 
Another stem, the potato, growing underground, forms one of 
man's staple articles of diet in this country. 

Practical Exercise 2. Fill out a second column in your table with ten dif- 
ferent stems used as food. 

Roots as food. Roots which store food for plants form an impor- 
tant part of man's vegetable diet. Beets, radishes, carrots, pars- 
nips, sweet potatoes, and many others might be mentioned. 



522 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 




Wright Pierce 
Read the table below and tell which of these roots contains the most nutrients. 

The following table shows the proportion of nutrients in some 
of the more common roots : 





Water 


Proteins 


Carbo- 
hydrates 


Fat 


Mineral 
Matter 


Carrot . . . 
Parsnip . . . 
Turnip . . . 
Sweet potato 
Beet .... 


89 
81 
92.8 

74 
82.2 


0.5 
1.2 
0.5 
1.5 
0.4 


5 

8.7 

4. 
20.2 
13.4 


0.2 
1.5 
0.1 
0.1 
0.1 


1.0 
1.0 

0.8 
1.5 
0.9 



Practical Exercise 3. Add ten roots to your list of foods. Using the above 
table, figure out the roots which give you the most food for your money at 
current prices. 

Seeds as foods. Our cereal crops, corn, wheat, oats, etc., have 
played a very important part in the civilization of man and are 
now of much importance to him as food products. Bread made 



SEEDS AS FOODS 



523 




What seeds, other than those given here, do you use for food ? 



Wright Pierce 



from wheat flour is frequently called the " staff of life." Our 
grains are the cultivated progeny of wild grasses. Domestication 
of plants and animals marks epochs in the advance of civilization. 
The man of the stone age hunted wild beasts for food, and lived 
like one of them in a cave or wherever he happened to be ; he was 
a nomad, a wanderer, with no fixed home. He may have dis- 
covered that wild roots or grains were good to eat ; perhaps he 
stored some away for future use. Then came the idea of growing 
things at home instead of digging or gathering the wild fruits from 
the forest and plain. The tribes which first cultivated the soil 
made a great step in advance, for they had as a result a fixed place 
for habitation. The cultivation of grains and cereals gave them a 
store of food which could be used at times when other food was 
scarce. The word " cereal " was derived from Ceres, the Roman 
goddess of agriculture. From earliest times the growing of grain 
and the progress of civilization have gone hand in hand, A§ 



524 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



nations have advanced in power, their dependence upon the cereal 
crops has become greater and greater. 

" Maize, Indian corn, has played a most important part in the 
history of the New World, as regards both the red men and the white 
men. It could be planted without clearing or ploughing the soil. 
There was no need of threshing or winnowing. Sown in tilled land, 

it yields more than twice as 
much food per acre as any 
other kind of grain. This 
was of incalculable advan- 
tage to the English settlers 
in New England, who would 
have found it much harder 
to gain a secure foothold 
upon the soil if they had 
had to begin by preparing 
it for wheat or rye," says 
John Fiske. {The Discovery 
of America. Houghton 
Mifflin Co.) 

Today, in spite of the 
great wealth which comes 
from our mineral resources, 
live stock, and manufac- 
tured products, a very 
good index of our country's 
prosperity is the size of the corn and wheat crop. According to a 
recent report, the value of farm property in the United States is 
more than $57,000,000,000, a sum greater than that invested in all 
manufactures in the United States. 

Corn. Over 2,000,000,000 bushels of corn were raised in the 
United States during the year 1929. This figure is so enormous 
that it has but little meaning to us. Iowa and Illinois are the great- 
est corn-producing states in this country, each having a yearly 
record of over 300,000,000 bushels. The figure on page 525 shows 
the principal corn-producing areas in the United States. 

Indian corn has many uses. It is a valuable food. It has a 
large proportion of starch, from which corn syrup, starch, and 




Wright Pierce 
What part of the cauliflower is used for food ? 



GRAINS 



525 



alcohol are made. Machine oil and soap are made from corn grain. 
The leaves and stalks make excellent fodder or they can be made 
into paper and artificial silks. The husks are used in mattresses ; 
the cobs are used for fuel or ground up for meal for live stock ; and 
the pith in the stalk is used as a protective belt placed below the 
water line of our huge battleships. 




More corn is raised in certain areas of the United States than in other areas. 

account for this ? 



How can you 



Wheat. Wheat is the crop of next greatest importance in this 
country. Over 800,000,000 bushels were raised in this country in 
1929, representing a total money value of about 8840,000,000, 
although during the World War our farmers received over 
82,000,000,000 yearly for a crop of less than 1,000,000,000 bushels. 
Seventy-two per cent of all the wheat raised comes from the North 
Central States and the far West. Much of the wheat crop is 
exported, thus indirectly giving employment to thousands of people 
on railways and steamships. Wheat is used chiefly for manufac- 
ture into flour The germ, or young wheat plant, is sifted out dur- 
ing this process and made into certain breakfast foods. Flour 
making forms the chief industry of Minneapolis, Minnesota, and 
of several other large and wealthy cities in this country. 

Other grains. Of the other cereal grains raised in this country, 
oats is the most important crop, more than 1,200,000,000 bushels 



526 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

having been produced in 1929. Barley and rye, grains much like 
wheat, are produced in smaller quantity. One of the most impor- 
tant grain crops for the world is rice. The fruit of this grasslike 
plant, after threshing, screening, and milling, forms the principal 
food of probably one third of the human race. 



VW^^ 


"^s^h 




■;. ~*~~~~& Vl J ' J \J 


V' : ; \ / _ •.' / .' jfr ■.'•l^^;^m» 


S~\*' i ' V/^W 




Coch dot rtpt 
10.000 acn 





How can you account for the location of these wheat-producing areas in the United States ? 
Why is wheat such an important crop in this country ? 

Practical Exercise 4. Obtain from government publications or the World 
Almanac the following facts: (1) amount invested in manufactures for the 
current year; (2) amount invested in agriculture for the current year; 
(3) the size and value of the corn crop ; and (4) the size and value of the 
wheat crop. 

Practical Exercise 5. What agricultural products are raised in your com- 
munity? About what proportion of wealth is invested in agriculture as 
against manufactories? Do they raise any "corn on the hoof" in your 
community ? 

Practical Exercise 6. List in your table ten important grains used as foods. 
Give ten different uses of grains. 

Practical Exercise 7. If there is a flour mill in your locality, visit it and 
report to the class on your trip. 

Garden fruits and vegetables. Vegetables have come to play 
an important part in the diet of man. People are using more 
vegetables and less meat, and are more healthful and feel better 
for it. Market-gardening forms the lucrative business of many 
thousands of people near our great cities and in many of our south- 
ern states. Some of the important garden fruits are squash, 
cucumbers, pumpkins, melons, tomatoes, peppers, strawberries, 



ORCHARD AND OTHER FRUITS 



527 




Which of the above fruits are raised in your locality ? 



Wright Pierce 
What others are raised there ? 



raspberries, and blackberries. As many as 1000 carloads of melons 
were shipped from the Imperial Valley, California, during a single 
day in 1930. More than $165,000,000 worth of fruits are canned 
or dried each year in addition to what is sold fresh. Beans and 
peas are important as foods because of their relatively large amount 
of protein. Canning green corn, peas, beans, asparagus, toma- 
toes, etc., has become an important industry. 

Orchard and other fruits. In the United States an average of 
nearly 200,000,000 bushels of apples are grown every year. 
Peaches, pears, plums, 
apricots, and cherries 
also are raised in large 
orchards, especially in 
California and in 
Georgia. 

The grape crop of the 
world is commercially 
valuable, because of the 
beverage made from the 
juice and raisins pro- 
duced from the grapes. 
The culture of the citrus 
fruits, lemons, oranges, 
and grapefruit has in- 
creased in recent years 

J Wright Pierce 

because Of th§ di§COVery Why are citrus fruits valuable foods ? 



#.; / 


■ ** ■ > % 1 

1' 




h wfM 


L(V - :/ 











528 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

of their values as producers of vitamins. Figs, olives, and dates 
also are grown now in the Southwest ; they are staple foods in 
the Mediterranean countries and are sources of wealth to the 
people there, as are coconuts, bananas, and many other fruits in 
tropical countries. Nuts form one of our important articles of 
food, largely because of the great amount of protein contained 
in them. Walnut ranches are now very profitable, especially in 
California. 

Beverages and condiments. The coffee and cacao beans and 
the leaves of the tea plant, products of tropical regions, form the 
basis of very important beverages of civilized man. Black and 
red pepper, mustard, allspice, nutmegs, cloves, and vanilla are all 
products from various fruits and seeds of tropical plants. 

Practical Exercise 8. Report to the class on the current value of crops men- 
tioned in this problem. Which crop is most valuable in California, Washing- 
ton, Florida, Arizona, New York, Michigan? Consult government bulletin 
and World Almanac for information. 

Self-Testing Exercise 

(1), (2), and (3) are examples of leaves 

used as food ; (4), (5), and (6) are stems 

used as food (7) are the largest crops raised in our country. 

Fruits, as ........ (8), (9), (10), (11), and 

........ (12), are of great importance (13) is the largest 

cereal crop in the United States, with (14) a close second. 

PROBLEM II. WHAT ARE OTHER ECONOMIC VALUES OF 

PLANTS? 

Many of our industries would not be in existence were it not 
for certain plant products which furnish the raw materials. Many 
cities of the East and South, for example, depend upon cotton 
to give employment to thousands of factory hands. 

Cotton. Of all our native plant products cotton is probably of 
the most importance. More than twelve million bales of five 
hundred pounds each are raised annually. 

The cotton plant thrives in warm regions. The seeds of the 
fruit have long filaments attached to them. Bunches of these 



VEGETABLE FIBERS 



529 




Blossom and bolls of a cotton plant. 



filaments, after treatment or ginning, are easily twisted into threads 
from which are manufactured cotton cloth, such as muslin, calico, 
cretonne, and gingham. In addition to the fiber, cottonseed oil, 
a substitute for olive oil, is 
made from the seeds, the hulls 
are used for making artificial 
silk, rayon, and the refuse 
makes fodder for cattle. 

Other vegetable fibers. 
Among the other important 
vegetable fibers are Manila 
hemp, which comes from the 
leaf-stalks of a plant of the 
banana family, and true hemp, 
which is the bast or woody 
fiber of a plant cultivated in 
most warm parts of the earth. 
These fibers are used for twine 
or rope. Flax is another im- 
portant fiber plant, grown largely in Russia, Ireland, Belgium, and 
other parts of Europe. Flax is becoming a more important crop 
in this country although it is raised here chiefly for its seeds. Linen 
cloth is made from the bast fibers of the stem of this herb. Burlap 
and coarse bags are made from the fiber of the jute plant, raised 
in India. 

Vegetable oils. Some of the same plants which give fiber also 
produce oil. Cottonseed oil pressed from cotton seeds, linseed 
oil from the seeds of the flax plant, and coconut oil (the covering 
of the nut produces a fiber) are examples. One of the important 
industries of California is olive culture, the fruit being used as a 
table delicacy, while oil pressed from the fruit is used largely in 
salad dressings. 

Drug-producing plants. Quinine, the specific remedy for 
malaria, was known by the Indians in South America before the 
white men came. It is made from the bark of the cinchona tree. 
South America also furnishes us with cocaine, a habit-forming 
drug made from the leaves of the coca tree of Peru. Morphine 



530 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

and opium come from the poppy. Many of our pleasant oils and 
flavors, as eucalyptus, wintergreen, and peppermint, come from 
plants. 

Tobacco, although a poisonous plant because of the nicotine it 
contains, is, nevertheless, one of this country's largest crops. Over 
1,200,000,000 pounds were raised in 1927, having a total value of 
about $266,000,000. Atropine and belladonna, both poisons used 
as drugs, are from plants related to the tobacco. 

Practical Exercises 9. Make a table to show the value of the chief fiber 
crops in your section of the country during the past year. Get information 
from your local Chamber of Commerce. 

What other crops are of value in your locality and why ? 

The use of tobacco has greatly increased since the World War. Give three 
possible reasons why this is so. 

Self-Testing Exercise 

Our clothes lines are made from (1). Burlap bags are 

made from (2). Linen comes from (3). The 

coca tree gives us (4) (5), although a poisonous 

plant, is one of the largest crops we raise (6) is the most 

important fiber plant in this country. 

PROBLEM III. WHAT IS THE VALUE OF ANIMALS AS FOOD 

FOR MAN? 

Indirect use of animals as food. Just as plants form the food 
of animals, so some animals are food for others. Protozoa and 
many forms of tiny plants, known as plankton, which are swarm- 
ing near the surface of bodies of fresh and salt water, form the food 
supply of many forms of life. Many fish live on plankton or on 
smaller fish which feed on plankton. Some fishes, as the menhaden, 
the shad, and others, are provided with gill rakers by means of 
which they strain these minute organisms from the water. Other 
fishes are bottom feeders, as the blackfish and the sea bass, living 
almost entirely upon mollusks and crustaceans. Still others are 
hunters, feeding upon smaller species of fish, or even upon their 
weaker brothers. Such are the bluefish, the weakfish, the barra- 
cuda, and others. The right whale, the largest of all mammals, 
strains protozoa and other small animals and plants out of the 



MOLLUSKS AS FOOD 531 

water by means of hanging plates of whalebone or baleen, the slen- 
der filaments of which form a sieve from the top to the bottom of 
the mouth. 

In a balanced aquarium the plants furnish food for the tiny 
animals and some of the larger ones, for example, the snails. The 
smaller animals are eaten by the larger ones. The waste matter 
given off by the animals and their death and decay furnish the 
plants with the required nitrogen and other material. Thus we see 
the aquatic world is a great balanced aquarium. Man disturbs 
this ecological balance when, as in the Illinois River, he dumps his 
untreated sewage and factory wastes into the stream near its source. 
The immediate result has been the destruction of fish life for a dis- 
tance of about 100 miles. It has been estimated by Professor Forbes 
that the Illinois River, before it was polluted by the Chicago drain- 
age canal, produced annually over 150,000,000 pounds of fish food. 
On the other hand, diluted sewage in a river may be utilized by the 
bacteria which in turn are used by microscopic animals and these in 
turn by crustaceans and snails which form the food of fishes. 

Practical Exercise 10. Explain how living things in any body of water in 
your locality indirectly produce food for man. 

Direct use of animals as food ; lower forms. The forms of life 
lower than the mollusks are of little use directly as food, although 
the Chinese are very fond of sea cucumbers (page 227), which are 
preserved by drying and are called trepang. Sea urchins are eaten 
in the West Indies, under the name of " sea eggs." 

Mollusks as food. The oyster. The oyster industry is very 
profitable. Hundreds of boats and thousands of men are engaged 
in dredging for oysters. Three of the most important of our oyster 
grounds are Long Island Sound, Narragansett Bay, and Chesa- 
peake Bay. The western coast also produces oysters, but they are 
inferior to those of the eastern coast. 

Oysters are never found in muddy water, for they would be 
quickly smothered by the sediment. They cling to stones or 
shells or other objects which project a little above the bottom. 
Here food is abundant and oxygen is obtained from the air in the 
water surrounding them. Oyster raisers usually throw oyster 



532 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

shells into the water to provide places of attachment for the } T oung 
oysters. 

In some parts of Europe and of this country where oysters are 
raised artificially, stakes or brush are sunk in shallow water so 
that the young oysters, after the free-swimming stage, may find 
some object to which they can fasten and escape the danger of 
smothering in the mud on the bottom. After the oysters are a 
year or two old, they are taken up and transplanted in deeper water 




In some places, oysters are gathered by means of long-handled tongs. In other places, 

dredges are used. 



suitable for growth. At the age of three or four years they are 
ready for the market. 

Clams and scallops. Other mollusks used for food are clams 
and scallops. Two species of the former are known : one as the 
" round," another as the " long " or " soft-shelled " clam. The 
former (Venus mercenaria) was called by the Indians " quahog," 
and is still so called in the Eastern States. The blue area of its 
shell was used by the Indians to make wampum, or money. The 
quahog is now extensively used as food. The " long " clam (My a 
arenaria) is considered better than the round clam for food by the 
inhabitants of Massachusetts and Rhode Island. This clam was 
highly prized as food by the Indians. It has been introduced on 



CRUSTACEANS AS FOOD 



533 



the Pacific coast and is rapidly coming into favor there. Dredg- 
ing for scallops, another delicacy of the mollusk family, is an 
important industry along certain parts of our coasts. 

Practical Exercise 11. What mollusks are used for food in your locality? 
Find out by inquiry in local markets just where each comes from. 

If you live where shellfish are produced, make a report to the class on this 
industry. 

Why may raw oysters or clams be a source of disease ? 

Crustaceans as food. Crustaceans are of considerable value 
as food. The lobster is highly esteemed as food, but has become 
scarce as the result of overfishing. Laws have been enacted in 
most lobster-producing states against overfishing. Egg-carrying 




^V~ vr 




'S'-e.c* ls<sfctc* 



A lobster pot. The lobster crawls forward and swims backward. He crawls 
through the openings in the nets into the chamber containing the bait, but 
when he tries to leave by swimming backward he gets caught. 



lobsters must be returned to the water ; all smaller than six to ten 
and one half inches in length (the law varies in different states) 
must be put back ; and other restrictions are placed upon the tak- 
ing of these animals, in the hope of saving the race from extinction. 
The United States Bureau of Fisheries and several eastern states 
are now hatching out millions of little lobsters each year, keeping 
them until they are large enough to care for themselves and then 
liberating them. The spiny lobster of the western coast is also 
in danger of extinction through overfishing. In consequence a 
long closed season has been declared, from the first of March to 
the fifteenth of October of each year. This protects the females 
during the egg-laying season. 
h. bio— 35 



534 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

Several other common crustaceans used as food by man are near 
relatives of the crayfish. Among them are the shrimp and the 
prawn, thin-shelled, active crustaceans common along our coasts. 
In spite of the fact that they form a large part of the food supply 
of many marine animals, especially fish, they do not appear to be 
decreasing in numbers. 

Another edible crustacean of considerable economic impor- 
tance is the blue crab. Crabs are found inhabiting muddy bot- 
toms of salt water inlets ; in such localities they are caught in great 
numbers in nets or traps baited with decaying meat. They are, 
indeed, among our most valuable sea scavengers, although they are 
hunters of living prey also. The young crabs differ considerably 
in form from the adult. They undergo a complete metamorphosis. 
Immediately after molting or shedding of the outer shell, in order 
to grow larger, crabs are known as " shedders," or soft-shelled 
crabs, and are considered a great delicacy. On the western coast 
a large deep-sea crab is caught which is an excellent article of food. 

Practical Exercise 12. List all the crustaceans you know that are found 
in your locality. Which ones are directly or indirectly used for food ? 

Practical Exercise 13. Make a report on the lobster industry of the United 
States. (See Readers Guide or Herrick's The American Lobster, Bui. U. S. 
Fish Com. 1895.) 

Practical Exercise 14. If you have ever caught any kind of crustaceans, 
describe your methods to the class. 

Fish as food. Fish are used as food the world over. The pres- 
ent value of the yearly catch of the world is estimated at over 
$1,000,000,000. From very early times herring were caught by 
the Norsemen. Fresh- water fish, such as whitefish, perch, pick- 
erel, pike, and the various members of the trout family, are 
esteemed food and, especially in the Great Lake region, form impor- 
tant fisheries. But by far the most important food fishes are those 
which are taken in salt water. Here we have two types of fish- 
eries : those where the fishes come up a river to spawn, such as the 
salmon, sturgeon, or shad, and those where the fishes are taken on 
their feeding grounds in the open ocean. The eggs of the sturgeon 
are used in the manufacture of the delicacy known as caviare. 
Herring are the world's most important catch, though not in this 
country. The salmon of our western coast are taken to the value 



AMPHIBIA AND REPTILES AS FOOD 



535 



of over $45,000,000 a year. Cod fishing also forms an important 
industry, over 7000 men being employed and over $30,000,000 of 
codfish being taken each year in this country. 

Practical Exercise 15. Make a list of the different fishes found in a local 
market. Get and record price per pound in a column opposite name of fish. 
In a third column give approximate distance of local market from source of 
production. In fourth column give your reasons for price per pound of given 
fish. 

How do fish compare in economic importance with other animals used as 
food in your locality ? 

Amphibia and reptiles as food. Frogs live in streams and 
ponds in all sections of the eastern part of the United States and 
along the Mississippi 
valley. They are used 
to a great extent for 
food as their large hind 
legs are esteemed a 
great delicacy. Certain 
reptiles, as the iguana, 
a lizard-like animal, are 
used as food by people 
of other nations. Many 
of the edible salt-water 
turtles are of large size, 
the leatherback and the 
green turtle often 
weighing six hundred 
to seven hundred 
pounds each. The flesh 
of the green turtle and 
of the diamond-back 
terrapin, an animal found in the salt marshes along our south- 
eastern coast, is highly esteemed as food. Unfortunately for the 
preservation of the species, these animals are usually taken dur- 
ing the breeding season when they go to sandy beaches to lay 
their eggs. 

Practical Exercise 16. What amphibia or reptiles in your part of the 
country are used as food? 




Ewing Gallouuy 

This fishwheel is typical of many found along the Colum- 
bia River. Fifteen tons of salmon have been caught by 
such a wheel in one day. The fish in swimming upstream 
strike wire nets attached to the rim of the wheel, which in 
turning raises them in the air and throws them into the 
boats which are fastened near by. 



536 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



Honey and wax. The honeybee gathers nectar, which she 
swallows, keeping the fluid in her crop until her return to the hive. 

Here it is forced out into 
the cells of the comb. It 
is now thinner than honey. 
To thicken it, the bees 
swarm over the open 
cells, moving their wings 
very rapidly, thus evapo- 
rating some of the water. 
A hive of bees may make 
between 30 and 80 pounds 
Of honey during a season. 
Over 60,000,000 pounds of 
honey is produced in this 
country every year. 

Practical Exercise 17. Re- 
port on a trip to an apiary, or 
on a study of an observation 
beehive. 



Birds as food. Birds, 
both wild and domesti- 
cated, form part of our 
food supply. But our 
wild game birds are dis- 
appearing so rapidly that 
source of food. Our domestic 
etc., form an important food 




Bee colonies spread by swarming. If hives are not 
provided for the swarming bees, they will find homes 
for themselves in hollow places or on trees, as shown 
above. 



we cannot consider them as a 
fowls, chicken, turkeys, ducks, 
supply. Eggs of domesticated fowls are of great importance as 
food, and egg albumin is used for other purposes, such as clarify- 
ing sugars and coating photographic papers. 

Practical Exercise 18, Give a report on the different birds in your locality 
that may be used as food. 

Mammals as food. When we consider the amount of wealth 
invested in cattle and other domesticated mammals bred and used 
for food in this country, we see the great economic importance of 
these animals. In 1928 nearly $3,000,000,000 worth of meat-pro- 



ECONOMIC VALUES OF ANIMALS 537 

ducing animals were owned in the United States. The United 
States, Argentina, and Australia are the greatest producers of 
cattle. Other products, such as milk, butter, and cheese, are ob- 
tained from cows and goats. In this country many hogs are raised 
for food. Their meat is used fresh, salted, smoked as ham and 
bacon, and pickled. Sheep, which are raised in great quantities 
in Australia, Argentina, Russia, Uruguay, and this country, are 
one of the world's greatest meat supplies. Deer, many game 
animals, seals, walruses, etc., are available as food for people in 
certain parts of the earth. 

Practical Exercise 19. From the information obtained from your local 
Chamber of Commerce or other sources, make a report to the class on the 
value of food mammals in your community. 

Self-Testing Exercise 

(1) and (2) are important shellfish used as food. 

Crustaceans used as food are (3), (4), and 

(5) (6) made from the nectar of flowers by the (7) 

is an important foodstuff. The (8) catch of food fishes is 

estimated to be over (9) . While birds are important as 

food, (10) are by far the most important food producers 

Most large animals (11) upon (12) ones. Factory 

(13) may not safely be dumped into (14) as they 

(15) the fish there. The right whale lives upon (16) 

animals which it (17) out of the water by means of hanging 

plates of (18). 

PROBLEM IV. WHAT ARE OTHER ECONOMIC VALUES OF 

ANIMALS? 

Domesticated animals. The domestication of the dog, the cow, 
the sheep, and especially of the horse, marks epochs in the advance 
of civilization. Beasts of burden are used the world over : horses 
almost everywhere ; certain cattle, as the water buffalo, in tropical 
Malaysia ; and camels, goats, and the llamas in some other coun- 
tries. 

Practical Exercise 20. Obtain from local sources the approximate value of 
domesticated animals in your locality, and tell why you think your figures 
are accurate. 



538 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



Bl p 


*-. r'jj 




^ : ^>w3SCfsBJJl 


^^^^^H 

^^B 


Riliil 







C. Ctarfce 



Two female silkworm moths and some of the eggs they have laid. 







£ ) B 







A tray of well-developed silkworm larvae feeding on mulberry leaves. They rarely leave their 
box containing food until they are ready to search for a place to spin their cocoons. 



THE SILKWORM 



539 




A mass of silkworm cocoons among the branches of a mulberry tree. 




A raw cocoon and a silken skein that has been made from the raw material. Can you 
describe the process by which silk thread is made from the silk in the cocoon? 



540 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



Uses of animal fibers. Pure silk goods are manufactured from 
raw silk, which is a fiber produced by the silkworm, the caterpillar 
of a moth. It lives on mulberry leaves and makes a cocoon from 
which the silk is obtained. China, Japan, Italy, and France, be- 
cause of cheap labor, are successful silk-raising countries. But 
the manufacture of silk goods, from imported raw silk, is still one 
of our great industries in spite of the production of rayon, one 
kind of artificial silk produced from wood pulp. 

There are in this country more than 1000 woolen mills, with 
nearly 200,000 wage earners. They produce, yearly, woolen and 
worsted goods valued at about $900,000,000. These mills use both 

domestic and im- 
ported wool. Nearly 
45,000,000 sheep are 
raised in this country 
for their wool. 

Goat's hair, espe- 
cially that of the 
Angora and of the 
Cashmere goats, 
camel's hair, and 
alpaca are much 
used in the clothing 
industries. 

Practical Exercise 21. 
Give a brief report on 
any of your local indus- 
tries which use animal 
fibers. 

Furs. The furs of 
many domesticated 
and wild animals, 
especially the carni- 
vores, are of much 
economic impor- 
tance. The Alaskan 
fur seal fisheries, which once amounted to millions of dollars annu- 
ally, have greatly decreased because of over-killing of the seals. 




Bureau of Biol. Survey 
The skunk is now raised for its valuable fur. 



PERFUMES 541 

Only about 25,000 seals were killed in 1928. Otters, skunks, sables, 
weasels, foxes, and minks are of considerable importance as fur 
producers. Even cats are now used, the fur usually masquerad- 
ing under some other name. The fur of the beaver, one of 
the largest of the rodents or gnawing mammals, is now difficult to 
procure, but fur of considerable value is obtained from the muskrat, 
squirrel, rabbits, and other rodents. The furs of the rabbit and 
nutria are used in the manufacture of felt hats. The quills of the 
porcupine (greatly developed and stiffened hairs) have a slight 
commercial value for decorative purposes. 

Animal oils. Whale oil, obtained from the " blubber " of 
whales, and formerly used for illumination, is now much used as a 
lubricating oil. Neat's-foot oil comes from the feet of cattle and 
is used for lubrication. Tallow from cattle and sheep, and lard 
from hogs, have so many well-known uses that comment is 
unnecessary. Cod-liver oil from the codfish is used medically. 
Much oil is obtained also from the menhaden of the Atlantic 
coast, which is used in dressing leather and making paints. Men- 
hadens are also used in great quantities for fertilizers. 

Hides, horns, hoofs, etc. Leather made from the skins of 
cattle, horses, sheep, goats, alligators, and snakes is used for shoes, 
pocketbooks, coats, gloves, and for many purposes. Leather 
manufacture is one of the great industries of the Eastern states, 
hundreds of millions of dollars being invested in manufacturing 
plants. Horns and bones are utilized for making combs, buttons, 
handles for brushes, etc. Glue is made from the animal matter 
in bones, horns, and hoofs. Ivory, obtained from the tusks of the 
elephant, walrus, and other animals, forms a valuable commercial 
product. It is largely used for knife handles, piano keys, and 
combs. 

Perfumes. The musk deer, musk ox, and muskrat furnish a 
valuable perfume called musk. Civet cats also give us a somewhat 
similar perfume. Ambergris, a basis for delicate perfumes, is 
formed in the intestines of the sperm whale. 

Practical Exercise 22. Tabulate the various products, other than meat, that 
are obtained from animals. In the next column indicate the ones used in your 
local industries. In the last column show uses of raw products to man. 



542 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



Direct use of protozoans. The protozoans have played an impor- 
tant part in rock building. Chalk beds and limestone rocks are 
made up to a large extent of the tiny skeletons of protozoans 
called foraminifers. The skeletons of some species are used to 
make a polishing powder. 

Sponges and coral. The sponges of commerce are the skeletons 
of animals that live attached to the bottom of the sea, and are 
composed of tough fibers of a material somewhat like that of a 
cow's horn. This fiber is elastic and has the power to absorb 

water. The warm waters 
of the Mediterranean Sea 
and the West Indies fur- 
nish most of our sponges. 
The sponges are pulled up 
from their resting places 
on the bottom by means 
of long-handled rakes 
operated by men in boats, 
or they are secured by 
divers. They are then 
spread out on the shore in 
the sun, and the living 
tissues allowed to decay. 
Then after treatment con- 
sisting of beating, bleach- 
ing, and trimming, the 
bath sponge is ready for 
the market. 

Some forms of coral, the 
skeleton of marine organ- 
isms, are of commercial 
value. The red or pre- 
cious coral of the Mediter- 
ranean Sea is highly prized 
for ornamental purposes. 
Pearls and mother-of-pearl. Pearls are prized the world over. 
Most of the finest come from the oysters and clams in the waters 




§§§§ 



e e © eoeo 



The pearl-like shells of fresh-water mussels are used 
in button-making. These mussels are extensively 
cultivated in the United States for this purpose. 



VALUE OF SNAKES 



543 



around Ceylon. It seems likely that the most perfect pearls are 
due to the growth within the mantle of the clam or oyster of cer- 
tain parasites which are stages in the development of a fluke worm. 
The irritation thus set up 
in the tissue causes mother- 
of-pearl, the substance 
that lines the interior of 
the shell, to be deposited 
around the source of irrita- 
tion, with the subsequent 
formation of a pearl. 

The pearl-button in- 
dustry in this country is 
largely dependent upon 
the fresh-water mussel, 
the shells of which are 
used. This mussel was 
being so rapidly depleted 
that the national govern- 
ment has worked out a 
means for its artificial 
propagation. 

Usefulness of the toad. 
The toad is of great eco- 
nomic importance to man 
because of its diet. No 
less than eighty-three 

species of insects, mostly injurious, have been proved to enter into 
the toad's diet. A toad has been observed to snap up 128 flies 
in half an hour. Thus it could easily destroy very many insects 
during a day and do an immense service to the garden during the 
summer. Toads also feed upon slugs and other garden pests. 

Value of snakes. Probably the most disliked and feared of all 
animals are the snakes. This feeling, however, is rarely deserved, 
for, on the whole, our common snakes are beneficial to man. The 
black snake, gopher snake, and milk snake feed largely on 
injurious rodents (rats, mice, etc.), the green garden snake eats 




Wright Pierce 

Chuckwalla — a stout-bodied lizard of the deserts 
of southwestern United States. It feeds on the buds 
and flowers of plants. Its flesh is used by some 
people for food. 



544 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

injurious insects, and the little DeKajr snake feeds partly on slugs. 
If it were not that the rattlesnake and copperhead are venomous, 
they also could be said to be useful, for they devour English 
sparrows, rats, mice, moles, and rabbits. 

Practical Exercises 23. Classify the animals mentioned in the preceding 
sections as to direct or indirect economic importance. Add as much as you can 
to the list. 

Make a list of all the ways in which animals living in your environment 
help indirectly to make you comfortable. 

Food of herbivorous animals. We must not forget that other 
animals besides insects and birds help to keep down the rapidly 
growing weeds. Herbivorous animals the world over devour, 
besides the grass which they eat, untold multitudes of weeds, 
which, if unchecked, would drive out the useful plants of the 
pastures, the grasses and grains. 

Self- Testing Exercise 

Animals furnish us with . (1), (2), (3), 

and (4) for clothing. Animal oils are obtained from the 

(5), (6), (7), and (8). Ivory is 

made from the (9) of QO) ; glue from (11) 

and (12) ; leather from the skins of (13), (14), 

and (15) ; perfumes from (16) (17) ; and 

pearls from (18). Coralis used for (19) (20). 

Sponges are (21) (22). The toad (23) 

(24). Most snakes are (25) to man. 



PROBLEM V. WHAT HARM IS DONE BY ANIMALS? 

Animals destructive to other animals used as food. Directly or 
indirectly, animals, in their struggle for life, destroy quantities of 
plants and other animals, that man uses as food. Starfish are 
enormously destructive to young clams and oysters, as the follow- 
ing evidence, collected by Professor A. D. Mead, of Brown Uni- 
versity, shows : A single starfish was confined in an aquarium 
with fifty-six young clams. The largest clam was about the 
length of an arm of the starfish, the smallest about ten millimeters 
in length. In six days every clam in the aquarium had been 



DESTRUCTIVE ANIMALS 545 

devoured. Hundred of thousands of dollars' damage is done 
annually to oysters in Connecticut alone by the ravages of star- 
fish. During the breeding season of clams and oysters, the boats 
dredge up tons of starfish which are thrown on shore to die or to 
be used as fertilizer. 

The liver fluke kills thousands of sheep every year. Tapeworms 
in cattle and trichina in hogs spoil much valuable food. Round- 
worms enter the bodies of food fish as parasites and kill large 
numbers annually. Boring mollusks, such as the whelk, destroy 
multitudes of other mollusks as food. Parasitic insects abound 
which kill useful insects, some of which, like the honeybee, pro- 
duce food. We can hardly estimate the harm done by one-celled 
parasites and their carriers, the ticks, mites, etc., for they are 
enormously destructive to cattle. 

Fish feed upon crustaceans and mollusks. The dogfish, shark, 
and other elasmobranchs destroy many lobsters, crabs, and 
other crustaceans, while many bottom-feeding fish eat mollusks. 
Fish are cannibals also, eating the eggs and young of their own 
kind. Salmon eggs are a favorite food of the western trout. 
Birds eat many fish and much other food. Large numbers of fish 
are killed by minks, otters, seals, and other fishing mammals. 
At one time it was estimated that an annual loss of fish equal to 
$20,000,000 was caused by carnivorous animals, such as wolves, 
coyotes, and others. But this amount is rapidly decreasing. 

Practical Exercise 24. Make a table to show the kinds of damage done by 
the animals common to your locality. Can you estimate the loss in dollars 
and cents? Get information from local farmers, cattle and sheep raisers, 
and your Chamber of Commerce. 

Rats as pests. David E. Lantz of the Bureau of Biological 
Survey is authority for the statement that the rat is the most 
destructive mammal in the world. He estimated the actual 
money loss from destruction of property by rats each year in this 
country to be over $200,000,000. Rats destroy the timber in 
houses, they cause fires by gnawing matches, they destroy great 
quantities of standing grain and stored food, they kill myriads of 
young chickens and other poultry and untold numbers of young 
birds. Worst of all, they spread diseases, especially bubonic 



546 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 





mm 

m-m 









plague. The fighting 
of rats alone, in the 
epidemics of plague in 
this country, has cost 
millions of dollars. 
They can be and must 
be exterminated. 

Practical Exercise 25. 

Make a report on methods 
of control of rats and mice 
in your community. Con- 
sult Lantz, House Rats 
and Mice, and Farmers 
Bulletin 896, United States 
Department of Agricul- 
ture. 

Bureau of Biological Survey CatS. Many Cats 

The rat is an enemy of the farmer. Notice the damage «^re kept as DetS and 
that he has done in this corn crib. " ' F > 

many run wild. Cats 
of both kinds do much injury by killing birds. Forbush, former 
state Director of Ornithology of the State of Massachusetts, esti- 
mated that they killed in New England as many as 1,500,000 birds 
annually, while Fisher says 3,500,000 birds is the annual toll for 
New York State. While this number seems almost impossible to 
believe, 226 cats under observation in Massachusetts have been 
known to kill 624 birds in one day. Cats also spread disease germs. 

Animals that prey upon man. The toll of death from animals 
which prey upon or harm man directly is relatively small. Snakes 
in tropical countries kill many cattle and not a few people. The 
dreaded cobra of India has a record of over 250,000 persons killed 
in thirty-five years. The loss of life from snake bites should soon 
be much reduced, thanks to the manufacture of antitoxin serums 
made to counteract the venom of poisonous snakes. 

Alligators and crocodiles feed not only on fishes, but often 
attack large animals, as horses and cows, and even man. The 
crocodiles of the Ganges River in India levy a yearly tribute 
of many hundred lives from the natives. 

Carnivorous animals which are not domesticated, such as lions 
and tigers, still inflict damage in certain parts of the world, but as 



BIRDS EAT INSECTS 



547 



the tide of civilization advances, their numbers are slowly but 
surely decreasing, so that as important factors in man's welfare 
they may be considered almost negligible. 

Practical Exercises 26. What harm is done in your locality by any of the 
above-mentioned animals ? How can cats be kept from killing birds ? Give 
all the reasons you can for and against keeping cats. What agencies control 
the harmful animals in your state ? 

Self-Testing Exercise 

Many oysters are destroyed annually by (1). Rats 

destroy thousands of dollars' worth of (2) for (3) 

every year. Many fishes are killed by (4) (5), 

(6), and (7) (8). Animals that are known 

to attack men are the (9), (10), (11), and 

(12). 



PROBLEM VI. WHAT IS 



THE ECONOMIC IMPORTANCE OF 
BIRDS? 



Birds eat insects. The food of birds . makes them of great 
importance to agriculture in our country. A large part of the diet 




L. W. Brownell 



If birds cannot get insects they eat grains. Some birds seem to prefer insects to seeds. 
Here is the remains of an ear of corn after Here is a young thrasher receiving a cater- 
a crow has eaten. pillar. 



548 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



of many of our native birds includes insects harmful to vegetation. 
Investigations undertaken by the United States Department of 

Agriculture (Division of 
Biological Survey) show 
that a surprisingly large 
number of birds, once 
believed to harm crops, 
really perform a service 
to farmers by killing in- 
jurious insects. Even 
the much maligned crow 
eats mice and harmful 
insects as well as grain 
and fruit. Swallows in 
the southern states kill 
the cotton boll weevil, 
one of our worst insect 
pests. Our earliest 
visitor, the bluebird, in- 
cludes grasshoppers, ants, 
spiders, weevils, tent 
caterpillars, army worms, 
cutworms, and the cod- 
ling moth in its diet. 
The robin, whose pres- 
ence in the cherry tree 
we resent during the spring and early part of the summer, 
includes all of the above and several other pests in its diet. It 
has a 95 per cent insect diet until June, and after that time about 
40 per cent of its food is insects. Many birds vary their diet, 
using the food substances which are most abundant around 
them. The swifts or swallows eat flies, the cuckoos and blue 
jays eat hairy caterpillars, which are eaten by few other birds; 
and much of the winter food of the chickadees consists of eggs 
of aphids or plant lice. Ants are eaten by many species of 
birds ; beetle larvae are preferred by crows, blackbirds, and 
robins. A pair of nesting robins were observed to dig out and eat 




ITICOXI 



.spcfx-r-o'v^ 



The food of some of our most familiar birds, 
these birds should be protected? 



Which of 



BIRDS EAT WEED SEEDS 



549 



from 50 to 70 cutworms and earthworms in one day. Many 
observations of the feeding of young birds by their parents indicate 
that birds eat a large amount of food in proportion to their size 
and consequently destroy vast numbers of injurious insects. 
Some idea of the amount of food eaten may be had from the data 
given by Professor Hodge. He says a pair of house wrens, very 
tiny birds, were observed to feed their five nestlings 230 insects, 
mostly large cabbage caterpillars, in one day. A young robin 
three weeks old ate 70 cutworms in one day ; a young tanager, 150 
cutworms in a day besides other food ; and a young phoebe just 
out of the nest, as many as 200 good-sized grasshoppers in a day. 
Without the birds the farmer would have a hopeless fight 
against insect pests. The effect of killing native birds in great 
numbers is now well seen in Italy and Japan, where insects have 
increased and do great damage to crops and trees. 

Practical Exercise 27. List the names of all birds that you know. Make a 
table for your workbook, giving the harm and value to man of each bird. 

Birds eat weed seeds. Not only do birds aid man in his battles 
with destructive insects, but nearly 300 species of birds eat the 
seeds of weeds 
also. Our native 
sparrows (not the 
English sparrow), 
the mourning 
dove, bobwhite, 
rose-breasted 
grosbeak, horned 
lark, crow black- 
bird, and other 
birds feed largely 
upon the seeds of 
many of our com- 
mon weeds. An 
examination of 
the stomachs of a 
number of these 

H. BIO — 36 




Wright Pierct 
What is the economic importance of the owl ? 



550 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



birds showed that they had consumed over one hundred kinds 
of weed seeds. The Biological Survey estimated that the 
various seed-eating native sparrows saved the farmer the sum of 
,260,000 in 1910. The tree sparrows alone in the state of 

Iowa are estimated to eat 
875 tons of weed seeds 
every winter. Not all 
birds are seed or insect 
eaters. 

Other foods of birds. 
Some, as the cormorants, 
ospreys, gulls, and terns, 
are active fishers. Near 
large cities especially, gulls 
act as scavengers, destroy- 
ing much floating garbage 
that otherwise might be 
washed ashore to become 
a menace to health. The 
buzzards of the West and 
South, and the vultures of 
India and semi-tropical 
countries, are of immense 
value as scavengers. Birds 
of prey (hawks and owls, 
eat living mammals, in- 
cluding many harmful 
rodents, as gophers, field mice, and rats. The Biological Survey 
has estimated that owls and hawks are worth about $20 apiece a 
year to the farmer because of the field mice they eat. 

Geographical distribution and migrations. Most of us are aware 
that some birds remain in a given region during the whole year, 
while other birds appear with the approach of spring, and depart 
southward with the warm weather in the fall of the year. Such 
birds we call migrants, while those that remain in one place the 
year round are called residents. For any one locality the migrants 
fall into three groups : those that arrive in the spring from the 




The golden plover spends the summer in the north- 
ern part of North America and the winter in the south. 
Explain why it takes a different route north in the 
spring from the one it takes south in the fall. 



SOME COMMON BIRDS 551 

south and remain until fall are called summer residents; those that 
come south during the winter for food and to escape the severe 
cold are called winter residents; and those that remain only a few 
days or a week in a locality when passing to the north or south 
are called transients. 

In Europe, where the problem of bird migration has been studied 
carefully, migrations appear to take place along well-defined paths. 
These paths usually follow the coast very exactly, although in 
places they may take the line of the coast that existed in former 
geological times. In this country the Mississippi valley forms one 
line of migration, while the north Atlantic seacoast forms another 
route. Just why birds migrate is not fully known. Evidently food 
shortage in the fall starts them on the path southward, but why 
they return is not so clear. They seem to have some instinct 
which brings them back year after year to the same nesting places. 

Self-Testing Exercises 

Mark in your workbook the correct statements : 
T. F. 1. Few birds are entirely useful. 

No insect pest can be entirely controlled by birds. 

Birds feed on the food that is most abundant at the time. 

Robins do more harm than good, for they eat our cherries. 

Birds of prey are scavengers. 

Most of our migrants, as the finches, warblers, and 
swallows, feed upon harmful insects. 

T. F. 7. Most owls are harmful because they feed upon rodents. 

PROBLEM VII. HOW CAN WE RECOGNIZE SOME COMMON 

BIRDS? 

It has been estimated that during the year there are between 
100 and 500 species of birds to be found in localities in various 
parts of the United States. The desert regions of the Southwest 
naturally have the fewest, the eastern seaboard states may have 
200 to 300, while there have been about 500 species identified in 
the northern and central parts of California. 

Field Exercise. Make a survey of your neighborhood to find out 
the number of different birds that are residents or migrants there. 



T. F. 


2. 


T.F. 


3. 


T.F. 


4. 


T.F. 


5. 


T.F. 


6. 



552 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 




C. Clarke 
Of what economic value is the robin? 



The following descrip- 
tions will help one to 
recognize a few of our 
common birds which are 
of decided economic value 
or harm. The size, color 
markings, food, and fa- 
miliar habits of some of 
our common birds will be 
given, with a brief state- 
ment of the reason why 
they are man's friends or 
enemies. 

Robin. A bird known 
to all of us makes an 
excellent type for com- 
parison with other less- 
known birds. The robin 
is nine to ten inches long. The male is brownish gray above, 
tinged with olive, with brown wings, and black on the head 
and the tail. The throat is light gray with black spots, and the 
breast is brownish red. The female is similar but darker in color. 
The robins live near houses and in orchards and make their nests 
of grass and mud, in trees or on buildings. The robin is a true 
thrush, whose pleasing song delights us in early spring. Its eco- 
nomic value is often discussed as it eats much fruit early in the 
season. Its diet usually consists of about 40 per cent insects, 
most of which, as ground beetles, caterpillars, plant lice, and cut- 
worms, are harmful. From February to May, in the east, its food 
is almost entirely insects. The western robin has done damage 
to olive and other fruit orchards when insect food was scarce, 
but like its eastern relative, it consumes a large percentage of 
insects most of the time. 

Bluebird. This is one of our earliest migrants. Its cheery 
note and blue coat are easily recognized. It is six and one half 
to seven inches in length. The male is bright blue above, and 
chestnut underneath. The female is duller in color. It nests in 



CHICKADEE 



553 



holes in trees or posts and 
in bird houses. Its food 
consists from about 70 to 
90 per cent of insects, 
largely grasshoppers, 
beetles, spiders, and cater- 
pillars. 

Chickadee. This is a 
small bird, about five and 
a quarter inches long. It 
is often an all-year-round 
resident. The crown of 
the head and throat are 
black, the cheeks white, 
the back gray, and the 
abdomen usually a dirty 
white. Its food is about 
70 per cent insect and 30 



Brownell 
A bluebird and her young. 

per cent seeds in the summer. In the winter it devours large 
quantities of eggs laid by insect pests. One bird was found to 
have eaten more than 430 eggs of the plant louse in a single day. 
Professor Sanderson of Cornell University has estimated that they 





Chickadee serving lunch. 



L. W. Brownell 



554 MAN CONTROLS SIS ENVIRONMENT FOR WEALTH 




A house wren bringing a caterpillar to her young 



eat over 8,000,000,000 insects in Michigan every year. On that 
basis what good must they do in the United States ? The chicka- 
dee is certainly one of man's best bird friends. 

House wren. This little migrant nests around our homes. 
It is a great songster, and is a decided asset to us because of its 
varied diet of cutworms, spiders, weevils, and May flies. It has 
a 98 per cent insect diet. One wren was observed to catch 600 
insects in one day. Its worst enemies are cats and larger birds. 
A proper nesting box with a small entrance is one of its best means 
of protection. The house wren is not quite five inches long. The 
upper part is brown, the lower grayish brown and white. The wings, 
flanks, and tail are slightly barred. It can be recognized easily by 
its small size, coloring, incessant singing or chattering, and by the 
fact that its tail is frequently held erect when the bird is at rest. 

Song sparrow. Another of our earliest visitors is the song 
sparrow. The male is about six and one half inches long. It is 
brown above with the head reddish-brown with blackish streaks. 
A streak of gray runs through the center of the crown, and there 
is a characteristic brown stripe on the sides of the throat. The 
breast is streaked with brown on a white ground. Its nest is 
usually on the ground or in a low bush. It is a friendly bird 
and is often seen near houses, though it prefers moist areas farther 



PHOEBE 



555 



away from man. It eats some insects, but like most of the native 
sparrows it feeds mainly upon weed seeds. 

American goldfinch. This bright yellow songster is one of our 
most attractive birds. It is often called the wild canary. It is 
about five inches long. The male has a bright yellow body with a 
black cap, and black and white tail and wings. The female is 
brownish olive above and yellowish white beneath. The gold- 
finch eats seeds of weeds, preferring those of the dandelion and 
thistle, two of our greatest weed pests. 

Yellow warbler. A bird often confused with the goldfinch is the 
yellow warbler. Like all warblers, this is a small bird about five 
inches in length. Its color is yellow, with breast flecked with red- 
dish brown (it has no black on the head as does the goldfinch). 
It nests near houses in low trees or bushes. It is of much economic 
importance because of its preference for the browntail and gypsy 
moth caterpillars, and other enemies of the forest trees. It also 
eats cankerworms and insects injurious to crops. We are spend- 
ing millions of dollars every year to fight these pests, and the 
warblers, besides being beautiful birds, are helping us in this fight. 

Phoebe. Another tireless hunter of insect pests is the phoebe. 
This bird is a flycatcher, seizing insects on the wing. It builds a 




Insects are the preferred food of phoebes, 



mell 



556 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



nest of mud — often under old bridges, around barns, or some- 
times under a barn floor. Its food consists of browntail and 
gypsy moths, grasshoppers, cankerworms, beetles, flies, and in 
the South cotton-boll weevils. The phoebe is about seven inches 
long, dusky olive-brown above, yellowish white underneath, with 
wings and tail dusky. The head is slightly crested, and the bill 
and feet are black. It is one of our early visitors. 

Barn swallow. Another bird with nesting habits similar to 
those of the phoebe is the barn swallow, which makes a nest plas- 
tered to the rafters of a barn or outbuilding. While most birds 
decrease in number with the cutting of forests and the building of 
cities, the barn swallow has increased because it feeds on insects 
which live on crops in cleared fields. It eats moths of cutworms, 
codling moths, leaf cutters, and many flies, bugs, and beetles. In 
the South it is an enemy of the cotton-boll weevil. This swallow 
is between six and seven inches in length. It is dark steel blue 
above, with throat and upper breast chestnut ; the lower breast 

and abdomen buff. The tail 
is deeply forked, showing 
white markings when spread. 
Catbird. Another bird 
which nests near houses and 
prefers the company of man is 
the catbird. From early May 
to late October its various 
calls and songs are the de- 
light of all bird lovers, for it 
is a great mimic and somewhat 
of a tease. The catbird, al- 
though it eats much fruit, is 
an insect feeder and gives its 
young insect food. Like other 
birds, it eats the food most 
abundant at the time. Birds 
taken from a canker-infested 
orchard made insects 95 per cent of their diet, although normally 
they eat over 60 per cent fruit. A. catbird is about nine inches 




Brownell 



Catbird entering nest. 



DOWNY WOODPECKER 



557 



in length, and of a dark grayish color, with the top of head and 
the tail blackish, with a distinct chestnut patch under the tail. 

Downy woodpecker. The woodpeckers are familiar to most 
boys and girls because of their conspicuous color and their peculiar 
habits. The male downy 
woodpecker is six and a half 
inches long, black and white 
barred, with a patch of scarlet 
on the upper side of the neck. 
It runs quickly up and down 
the trunks of trees, tapping 
the wood to locate insect 
holes. The bill is strong, 
sharp at the end, and is used 
as a chisel in boring into wood. 
The tongue is spearlike, one 
to one and a half inches 
long, and is used to pull out 
the larvae which lurk beneath 
the bark. On the average 
about 65 per cent of the food of 
woodpeckers is insect, largely 

maple, birch, apple, and other borers. Woolly aphids, caterpillars, 
and chrysalids are also its prey. The woodpeckers, called sap- 
suckers, live up to their name and are said to cause a yearly damage 
of over $1,250,000 to the lumber industry. On the other hand, 
they destroy large numbers of insects injurious to the same trees. 

Flicker. This bird, a woodpecker, is twelve inches long. The 
male is brown above and golden yellow under the wings and tail, 
brown spots on breast, a scarlet crescent on back of the neck, and 
a black crescent on the breast. It has a white rump which is 
conspicuous in flight and makes an easily recognized mark. The 
flicker is generally useful, feeding upon plant lice, ants (which 
make up about 45 per cent of its food), grasshoppers, caterpillars, 
and weed seeds. Like other woodpeckers, it nests in hollow trees. 

Baltimore oriole. This bright-colored and attractive bird is 
about seven and one half inches long. The male has the upper 




L. W. Brownell 



Downy woodpeckers on a tree trunk. 



558 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



back, wings, and throat black, with the outer tail feathers, breast, 
and under parts orange. The female is not so brilliantly colored, 

being yellow instead of 
orange. The hanging 
nests of the oriole, often 
woven with bits of string, 
cloth, and other materials, 
are a common sight in 
elm trees near our homes. 
These birds prefer inhab- 
ited areas and, because 
of their protected nests, 
are increasing in spite of 
cats and the English spar- 
rows. They feed largely 
upon insects. As high as 
92 per cent insect diet 
has been recorded in the 
summer season. The 
cankerworm, tussock, 
browntail, and forest tent 
caterpillars were found in 
the stomachs of northern 
birds, while those examined in the south contained many cotton- 
boll weevils. 

Screech owl. This is a small owl and one of the most useful, 
as it feeds upon field mice and other small destructive rodents as 
well as upon some moths, caterpillars, and beetles. It is about as 
large as a quail, about nine and one half inches in length. Its 
general coloring is gray on the under parts and reddish brown above. 
The eye is yellow. It usually nests in hollow trees. 

Crow. Our common crow, a glossy black bird from sixteen to 
nineteen inches long, is one of the few birds that may do more 
harm than good. In the early spring the crow is useful, 80 per 
cent of its diet being insect larvae, such as wireworms and 
May beetle larvae. It also eats field mice, but later does much 
harm in the newly planted corn fields. In parts of the country 




A flicker at its nesting hole. The stiff tail helps to 
hold the bird in this position. 



BIRDS HARMFUL TO MAN 



559 



where they are most abundant 
they cause harm by killing 
useful birds. 

English sparrow. The Eng- 
lish sparrow is an example of 
a bird introduced for the pur- 
pose of insect destruction, 
that has done great harm 
because of its relation to our 
native birds. Introduced at 
Brooklyn in 1850 for the 
purpose of exterminating the 
cankerworm, it soon aban- 
doned a diet largely of insects 
in favor of one of grain and 
has driven out many of our 
native insect feeders. In- 
vestigations by the Depart- 
ment of Agriculture show that 
in the country these birds and 
their young feed to a large 
extent upon grain, thus show- 
ing them to be injurious to 
agriculture. Dirty and very 
prolific, they have long since 
worked their way from the 
East to the Pacific coast. 
The English sparrow has be- 
come a national pest, and 
should be exterminated in 
order to save our native birds. 

Birds harmful to man. 
While there are a few birds 
that do both harm and good, 
like the crow, catbird, blue 
jay, cedar waxwing, and robin, 
there are others that are bad, 




L. W. Brownell 
Is the screech owl a beneficial or harmful bird ? 
Why? 




W. Brownell 



A warbler feeding a young cowbird which is 
nearly as large as its foster mother. 



560 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 

and we can find little or no good to say about them. The English 
sparrow is the greatest bird pest, for reasons given above. The 
cowbird never builds a nest nor cares for her young. She lays 
her eggs in the nests of smaller birds, usually warblers, where later 
ihe young cowbirds cause the death of the rightful inhabitants of 
the nest. Cooper's hawk, the sharp-shinned hawk, and the great 
horned owl kill smaller, beneficial birds. 

Practical Exercise 28. Try to find a nest containing eggs and watch the de- 
velopment of the young over